I am doing a online code challenge that asks to write a anagram checker program. So i made the following the program and for some weird reason it's not passing all the test cases. I wrote a main function on my own and tried to test it myself and it seems to work fine.
#include<iostream>
using namespace std;
bool anagrams(string str1, string str2);
int main(){
string str1="abcd";
string str2="dcba";
cout<<anagrams(str1,str2)<<endl;
cin.get();
return 0;
}
bool anagrams(string str1, string str2){
if(str1.length()!=str2.length()) return false;
for(int i=0;i <str1.length(); i++){
for(int j=0;j<str2.length();j++){
if(str1[i]==str2[j]){
str1[i]='*';
break;
}
}
}
for(int i=0;i<str1.length();i++){
if(str1[i]!='*') return false;
}
return true;
}
It looks like your code checks if the characters in str1 exist in str2.
For example, if str1="abca" and str2="abcd" they are clearly not anagrams.
However won't it turn str1 into "****" since it will match the last a in str1 to the first a in str2 (twice).
Okay, so the program wouldn't work with inputs such as
abcc
abcd
So a quick fix would be marking the character from str2 with * as you iterate through each character in str1.
#include<iostream>
using namespace std;
bool anagrams(string str1, string str2);
int main(){
string str1="abcc";
string str2="dcba";
cout<<anagrams(str1,str2)<<endl;
cin.get();
return 0;
}
bool anagrams(string str1, string str2){
if(str1.length()!=str2.length()) return false;
for(int i=0;i <str1.length(); i++){
for(int j=0;j<str2.length();j++){
if(str1[i]==str2[j]){
str2[j]='*';
break;
}
}
}
for(int i=0;i<str2.length();i++){
if(str2[i]!='*') return false;
}
return true;
}
There are better algorithms out there for anagram checkers, such as sorting and using a hashable.
package com.datastructures.programs;
public class Anagram {
public static void main(String[] args) {
// TODO Auto-generated method stub
String s1 = "abcc";
String s2 = "abcd";
System.out.println(Anagram.isAnagram(s1, s2));
}
private static boolean isAnagram(String s1, String s2) {
// TODO Auto-generated method stub
int[] temp = new int[256];
boolean isAnagram = true;
if (s1.length() != s2.length()) {
return false;
}
for (char s : s1.toCharArray()) {
int index = (int) s;
temp[index]++;
}
for (char s : s2.toCharArray()) {
int index = (int) s;
temp[index]--;
}
for (int i = 0; i < 256; i++) {
if (temp[i] != 0) {
return false;
}
}
return true;
}
}
Related
I want to write myself a function similar to PHP's str_repeat. I want this function to add specified amount of characters at the end of string.
This is a code that does not work (string argument 2 expected!)
void chrrepeat(const char &ch, string &target, const int &count) {
for(int i=0; i<count; i++)
strcat(target, ch);
}
I don't exactly know what language is that (C++?), but you seem to be passing a char to strcat() instead of a null-terminated string. It's a subtle difference, but strcat will happily access further invalid memory positions until a null byte is found.
Instead of using strcat, which is inefficient because it must always search up to the end of the string, you can make a custom function just for this.
Here's my implementation in C:
void chrrepeat(const char ch, char *target, int repeat) {
if (repeat == 0) {
*target = '\0';
return;
}
for (; *target; target++);
while (repeat--)
*target++ = ch;
*target = '\0';
}
I made it return an empty string for the case that repeat == 0 because that's how it works in PHP, according to the online manual.
This code assumes that the target string holds enough space for the repetition to take place. The function's signature should be pretty self explanatory, but here's some sample code that uses it:
int main(void) {
char test[32] = "Hello, world";
chrrepeat('!', test, 7);
printf("%s\n", test);
return 0;
}
This prints:
Hello, world!!!!!!!
Convert char to string.
void chrrepeat(char ch, string &target, const int count) {
string help = "x"; // x will be replaced
help[0] = ch;
for(int i=0; i<count; i++)
strcat(target, help);
}
I want to create a 2 dimensional character array dynamically through pointers. Then input 10 strings in it and then take a string target from user and find it in array. if it is present then return its index. I have written code for it but it has errors. Please help me in correcting it. Thanks in advance.
#include<iostream>
#include<string>
using namespace std;
int strsearch(char [][50],char *);
int main()
{
char str[10][50];
char *target=new char [50];
int index;
for(int i=0; i<10; i++)
{
str = new char* [50];
str++;
}
for(int i=0; i<10; i++)
{
cout<<"Enter a sting";
cin>>str[i][50];
str++;
}
cout<<"Enter a string to find:";
cin>>target;
index=strsearch(str,target);
if(index<0)
{
cout<<"String not found";
}
else
{
cout<<"String exist at location "<<index<<endl;
}
return 0;
}
int strsearch(char string[10][50],char *fstr)
{
int slen;
for(int i=0;i<10;i++)
{
slen=strlen(**string);
if (strnicmp(*string[50],fstr,slen)== 0)
{
return i;
}
}
return -1;
}
Simply use:
std::vector<std::string> obj;
It will save you all the head & heart aches and guard you against easy to go wrong manual memory management issues. What you are trying to do is to solve the problem C way. With C++ the correct way to do it is using a vector of strings.
I think this is an error in any case:
for(int i=0;i<10;i++)
{
slen=strlen(**string);
if (strnicmp(*string[50],fstr,slen)== 0)
{
return i;
}
}
Must be something like:
for(int i=0;i<10;i++)
{
slen=strlen(string[i]);
if (strnicmp(string[i],fstr,slen)== 0)
{
return i;
}
}
I have done some correction, i think it can help you but i have not compiled to check for errors.
#include<iostream>
#include<string>
#define DIM_1 10 // Avoid to use "magic numbers" in your code
#define DIM_2 50
using namespace std;
int strsearch(char **string,char *fstr);
int main()
{
char **str = new char*[DIM_1]; //char str[10][50]; dynamically allocated array.
char *target=new char [DIM_2];
int index;
for(int i=0; i<DIM_1; i++)
{
str[i] = new char[DIM_2]; //Do not lost the original pointer
//str++;
}
for(int i=0; i<DIM_1; i++)
{
cout<<"Enter a sting";
cin>>str[i][DIM_2];
//str++; Do not lost the original pointer
}
cout<<"Enter a string to find:";
cin>>target;
index=strsearch(str,target);
if(index<0)
{
cout<<"String not found";
}
else
{
cout<<"String exist at location "<<index<<endl;
}
// Free memory!!
for (int i=0; i<DIM_1;i++) delete[] str[i];
delete[] str;
delete[] target;
return 0;
}
int strsearch(char **string,char *fstr) //its dinamicly allocated array
{
int slen;
int result=-1; //Only one return-> structured programming
for(int i=0;i<DIM_1;i++)
{
slen=strlen(**string);
//strlen and strnicmp is C, not C++, check string class.
if (strnicmp(string[i],fstr,DIM_2)== 0) //Find in the string[i]
{
result= i;
}
}
return result;
}
Here is the entire program, please help me, I've tried everything to find out what exactly is going with the memory. The problem is everything runs perfectly, but there are some extra characters printed with output.
Here is the .h file:
class MyString
{
public:
MyString();
MyString(const char *message);
MyString(const MyString &source);
~MyString();
const void Print() const;
const int Length() const;
MyString& operator()(const int index, const char b);
char& operator()(const int i);
MyString& operator=(const MyString& rhs);
bool operator==(const MyString& other) const;
bool operator!=(const MyString& other) const;
const MyString operator+(const MyString& rhs) const;
MyString& operator+=(const MyString& rhs);
friend ostream& operator<<(ostream& output, const MyString& rhs);
const int Find(const MyString& other);
MyString Substring(int start, int length);
private:
char *String;
int Size;
};
istream& operator>>(istream& input, MyString& rhs);
The .cpp file:
MyString::MyString()
{
char temp[] = "Hello World";
int counter(0);
while(temp[counter] != '\0')
{
counter++;
}
Size = counter;
String = new char [Size];
for(int i=0; i < Size; i++)
String[i] = temp[i];
}
//alternate constructor that allows for setting of the inital value of the string
MyString::MyString(const char *message)
{
int counter(0);
while(message[counter] != '\0')
{
counter++;
}
Size = counter;
String = new char [Size];
for(int i=0; i < Size; i++)
String[i] = message[i];
}
//copy constructor
MyString::MyString(const MyString &source)
{
int counter(0);
while(source.String[counter] != '\0')
{
counter++;
}
Size = counter+1;
String = new char[Size];
for(int i = 0; i <= Size; i++)
String[i] = source.String[i];
}
//Deconstructor
MyString::~MyString()
{
delete [] String;
}
//Length() method that reports the length of the string
const int MyString::Length() const
{
int counter(0);
while(String[counter] != '\0')
{
counter ++;
}
return (counter);
}
/*Parenthesis operator should be overloaded to replace the Set and Get functions of your previous assignment. Note that both instances should issue exit(1) upon violation of the string array bounaries.
*/
MyString& MyString::operator()(const int index, const char b)
{
if(String[index] == '\0')
{
exit(1);
}
else
{
String[index] = b;
}
}
char& MyString::operator()(const int i)
{
if(String[i] == '\0')
{
exit(1);
}
else
{
return String[i];
}
}
/*Assignment operator (=) which will copy the source string into the destination string. Note that size of the destination needs to be adjusted to be the same as the source.
*/
MyString& MyString::operator=(const MyString& rhs)
{
if(this != &rhs)
{
delete [] String;
String = new char[rhs.Size];
Size = rhs.Size;
for(int i = 0; i < rhs.Size+1 ; i++)
{
String[i] = rhs.String[i];
}
}
return *this;
}
/*Logical comparison operator (==) that returns true iff the two strings are identical in size and contents.
*/
bool MyString::operator==(const MyString& other)const
{
if(other.Size == this->Size) {
for(int i = 0; i < this->Size+1; i++)
{
if(&other == this)
return true;
}
}
else
return false;
}
//Negated logical comparison operator (!=) that returns boolean negation of 2
bool MyString::operator!=(const MyString& other) const
{
return !(*this == other);
}
//Addition operator (+) that concatenates two strings
const MyString MyString::operator+(const MyString& rhs) const
{
char* tmp = new char[Size + rhs.Size +1];
for(int i = 0; i < Size; i++)
{
tmp[i] = String[i];
}
for(int i = 0; i < rhs.Size+1; i++) {
tmp[i+Size] = rhs.String[i];
}
MyString result;
delete [] result.String;
result.String = tmp;
result.Size = Size+rhs.Size;
return result;
}
/*Addition/Assigment operator (+=) used in the following fashion: String1 += String2 to operate as String1 = String1 + String2
*/
MyString& MyString::operator+=(const MyString& rhs)
{
char* tmp = new char[Size + rhs.Size + 1];
for(int i = 0; i < Size; i++) {
tmp[i] = String[i];
}
for(int i = 0; i < rhs.Size+1; i++)
{
tmp[i+Size] = rhs.String[i];
}
delete [] String;
String = tmp;
Size += rhs.Size;
return *this;
}
istream& operator>>(istream& input, MyString& rhs)
{
char* t;
int size(256);
t = new char[size];
input.getline(t,size);
rhs = MyString(t);
delete [] t;
return input;
}
ostream& operator<<(ostream& output, const MyString& rhs)
{
if(rhs.String != '\0')
{
output << rhs.String;
}
else
{
output<<"No String to output\n";
}
return output;
}
/*MyString::Find that finds a string in a larger string and returns the starting location of the substring. Note that your string location starts from 0 and ends at length -1. If the string is not found, a value of -1 will be returned
*/
const int MyString::Find(const MyString& other)
{
int nfound = -1;
if(other.Size > Size)
{
return nfound;
}
int i = 0, j = 0;
for(i = 0; i < Size; i++) {
for(j = 0; j < other.Size; j++) {
if( ((i+j) >= Size) || (String[i+j] != other.String[j]) )
{
break;
}
}
if(j == other.Size)
{
return i;
}
}
return nfound;
}
/*MyString::Substring(start, length). This method returns a substring of the original string that contains the same characters as the original string starting at location start and is as long as length.
*/
MyString MyString::Substring(int start, int length)
{
char* leo = new char[length+1];
for(int i = start; i < start + length+1; ++i)
{
leo[i-start] = String[i];
}
MyString sub;
delete [] sub.String; sub.String = leo; sub.Size = Size;
return sub;
}
//Print() method that prints the string
const void MyString::Print() const
{
for(int i=0; i < Size; i++)
{
cout<<String[i];
}
cout<<endl;
}
The main.cpp file:
int main (int argc, char **argv)
{
MyString String1;
const MyString ConstString("Target string"); //Test of alternate constructor
MyString SearchString; //Test of default constructor that should set "Hello World".
MyString TargetString (String1); //Test of copy constructor
cout << "Please enter two strings. ";
cout << "Each string needs to be shorter than 256 characters or terminated by /\n." << endl;
cout << "The first string will be searched to see whether it contains exactly the second string. " << endl;
cin >> SearchString >> TargetString; // Test of cascaded string-extraction operator
if(SearchString.Find(TargetString) == -1) {
cout << TargetString << " is not in " << SearchString << endl;
}
else {
cout << TargetString << " is in " << SearchString << endl;
cout << "Details of the hit: " << endl;
cout << "Starting position of the hit: " << SearchString.Find(TargetString) << endl;
cout << "The matching substring is: " << SearchString.Substring(SearchString.Find(TargetString), TargetString.Length()-1)<<"\n";
}
return 0;
}
Running the program you get this:
Please enter two strings. Each string needs to be shorter than 256 characters or terminated by /
.
The first string will be searched to see whether it contains exactly the second string.
firstly
real
realt World is not in firstly
Please Help!!
try adding a '\0' at the end of your strings in your MyString::MyString(const char *message) constructor
#Sam's answer is correct. I'm going to add on to it to help you learn what's happening.
C and C++ strings are really character arrays that follow a convention that the string is terminated with \0, sometimes called NUL (not null), which is a character where all bits are 0.
Your code gets the first part right in that it creates an array of characters. However, you do not apply the convention that the string must be NUL terminated.
You then pass a string that does not follow the NUL termination convention to cout, which does follow that convention. In other words, it runs through the string, printing each character to stdout, until it happens across the character \0 in memory. It's actually fairly lucky that it terminates. If there were not a \0 in the character array it is outputing, it would just keep on going until reaching a memory address that does not belong to your program and failing with a segmentation fault.
I have to manage servos from a computer.
So I have to send manage messages from computer to Arduino. I need manage the number of servo and the corner. I'm thinking of sendin something like this : "1;130" (first servo and corner 130, delimeter ";").
Are there any better methods to accomplish this?
Here is my this code :
String foo = "";
void setup(){
Serial.begin(9600);
}
void loop(){
readSignalFromComp();
}
void readSignalFromComp() {
if (Serial.available() > 0)
foo = '';
while (Serial.available() > 0){
foo += Serial.read();
}
if (!foo.equals(""))
Serial.print(foo);
}
This doesn't work. What's the problem?
You can use Serial.readString() and Serial.readStringUntil() to parse
strings from Serial on arduino
You can also use Serial.parseInt() to read integer values from serial
Code Example
int x;
String str;
void loop()
{
if(Serial.available() > 0)
{
str = Serial.readStringUntil('\n');
x = Serial.parseInt();
}
}
The value to send over serial would be "my string\n5" and the result would be str = "my string" and x = 5
Note: Serial.available() inherits from the Stream utility class.
https://www.arduino.cc/reference/en/language/functions/communication/serial/available/
This is a Great sub I found. This was super helpful and I hope it will be to you as well.
This is the method that calls the sub.
String xval = getValue(myString, ':', 0);
This is The sub!
String getValue(String data, char separator, int index)
{
int found = 0;
int strIndex[] = {
0, -1 };
int maxIndex = data.length()-1;
for(int i=0; i<=maxIndex && found<=index; i++){
if(data.charAt(i)==separator || i==maxIndex){
found++;
strIndex[0] = strIndex[1]+1;
strIndex[1] = (i == maxIndex) ? i+1 : i;
}
}
return found>index ? data.substring(strIndex[0], strIndex[1]) : "";
}
Most of the other answers are either very verbose or very general, so I thought I'd give an example of how it can be done with your specific example using the Arduino libraries:
You can use the method Serial.readStringUntil to read until your delimiter from the Serial port.
And then use toInt to convert the string to an integer.
So for a full example:
void loop()
{
if (Serial.available() > 0)
{
// First read the string until the ';' in your example
// "1;130" this would read the "1" as a String
String servo_str = Serial.readStringUntil(';');
// But since we want it as an integer we parse it.
int servo = servo_str.toInt();
// We now have "130\n" left in the Serial buffer, so we read that.
// The end of line character '\n' or '\r\n' is sent over the serial
// terminal to signify the end of line, so we can read the
// remaining buffer until we find that.
String corner_str = Serial.readStringUntil('\n');
// And again parse that as an int.
int corner = corner_str.toInt();
// Do something awesome!
}
}
Of course we can simplify this a bit:
void loop()
{
if (Serial.available() > 0)
{
int servo = Serial.readStringUntil(';').toInt();
int corner = Serial.readStringUntil('\n').toInt();
// Do something awesome!
}
}
You need to build a read buffer, and calculate where your 2 fields (servo #, and corner) start and end. Then you can read them in, and convert the characters into Integers to use in the rest of your code. Something like this should work (not tested on Arduino, but standard C):
void loop()
{
int pos = 0; // position in read buffer
int servoNumber = 0; // your first field of message
int corner = 0; // second field of message
int cornerStartPos = 0; // starting offset of corner in string
char buffer[32];
// send data only when you receive data:
while (Serial.available() > 0)
{
// read the incoming byte:
char inByte = Serial.read();
// add to our read buffer
buffer[pos++] = inByte;
// check for delimiter
if (itoa(inByte) == ';')
{
cornerStartPos = pos;
buffer[pos-1] = 0;
servoNumber = atoi(buffer);
printf("Servo num: %d", servoNumber);
}
}
else
{
buffer[pos++] = 0; // delimit
corner = atoi((char*)(buffer+cornerStartPos));
printf("Corner: %d", corner);
}
}
It looks like you just need to correct
foo = ''; >>to>> foo = "";
foo += Serial.read(); >>to>> foo += char(Serial.read());
I made also shomething similar..:
void loop(){
while (myExp == "") {
myExp = myReadSerialStr();
delay(100);
}
}
String myReadSerialStr() {
String str = "";
while (Serial.available () > 0) {
str += char(Serial.read ());
}
return str;
}
This code reads string until it sees '>' character
void loop() {
// put your main code here, to run repeatedly:
String msg = getMessage();
}
String getMessage() {
String msg = "";
while (Serial.available()>0) {
msg = Serial.readStringUntil('>');
}
return msg;
}
It's universal parser
struct servo
{
int iServoID;
int iAngle;
};
std::vector<std::string> split(const std::string& str, const std::string& delim)
{
std::vector<std::string> tokens;
size_t prev = 0, pos = 0;
do
{
pos = str.find(delim, prev);
if (pos == std::string::npos) pos = str.length();
std::string token = str.substr(prev, pos-prev);
if (!token.empty()) tokens.push_back(token);
prev = pos + delim.length();
}
while (pos < str.length() && prev < str.length());
return tokens;
}
std::vector<servo> getServoValues(const std::string& message)
{
std::vector<servo> servoList;
servo servoValue;
std::vector<std::string> servoString;
std::vector<std::string> values = split(message, ",");
for (const auto& v : values)
{
servoString.clear();
servoString = split(v, ";");
servoValue.iServoID = atoi(servoString[0].c_str()); //servoString[0].toInt();
servoValue.iAngle = atoi(servoString[1].c_str());// servoString[1].toInt();
servoList.emplace_back(servoValue);
}
return servoList;
}
to call:
std::string str = "1;233,2;123";
std::vector<servo> servos = getServoValues(str);
for (const auto & a : servos)
std::cout<<a.iServoID << " " << a.iAngle << std::endl;
Result
1 233
2 123
Modified the below circular queue code for my app.
This queue can hold 32 elements max and I have declared the elements as a structure array inside the class. For adding an element to the queue you have to call CreateElement() functions, which checks for a free element and returns an index. When I reuse an element after processing the following line in the CreateElement functions crashes
boost::shared_array<char> tData(new char[bufferSize]);
m_QueueStructure[queueElems].data = tData;
As per documentation, the assignment operator is supposed to destroy the earlier object and assign the new one. Why is it crashing? Can someone tell me where am I screwing?
#include "boost/thread/condition.hpp"
#include "boost/smart_ptr/shared_array.hpp"
#include <queue>
#define MAX_QUEUE_ELEMENTS 32
typedef struct queue_elem
{
bool inUse;
int index;
int packetType;
unsigned long compressedLength;
unsigned long uncompressedLength;
boost::shared_array<char> data;
}Data;
class CQueue
{
private:
int m_CurrentElementsOfQueue;
std::queue<Data> the_queue;
mutable boost::mutex the_mutex;
boost::condition_variable the_condition_variable;
Data m_QueueStructure[MAX_QUEUE_ELEMENTS];
public:
CQueue()
{
m_CurrentElementsOfQueue = 0;
for(int i = 0; i < MAX_QUEUE_ELEMENTS; i++)
{
m_QueueStructure[i].inUse = false;
m_QueueStructure[i].index = i;
}
}
~CQueue()
{
for(int i = 0; i < m_CurrentElementsOfQueue; i++)
{
int index = wait_and_pop();
Data& popped_value = m_QueueStructure[index];
popped_value.inUse = false;
}
m_CurrentElementsOfQueue = 0;
}
void push(Data const& data)
{
boost::mutex::scoped_lock lock(the_mutex);
the_queue.push(data);
lock.unlock();
the_condition_variable.notify_one();
}
bool empty() const
{
boost::mutex::scoped_lock lock(the_mutex);
return the_queue.empty();
}
bool try_pop(Data& popped_value)
{
boost::mutex::scoped_lock lock(the_mutex);
if(the_queue.empty())
{
return false;
}
popped_value=the_queue.front();
the_queue.pop();
return true;
}
int wait_and_pop()
{
boost::mutex::scoped_lock lock(the_mutex);
while(the_queue.empty())
{
the_condition_variable.wait(lock);
}
Data& popped_value=the_queue.front();
the_queue.pop();
return popped_value.index;
}
int CreateElement(int bufferSize, unsigned long _compressedLength,
unsigned long _uncompressedLength, int _packetType) /* Send data length for this function */
{
int queueElems = 0;
if(m_CurrentElementsOfQueue == 32)
{
CCommonException ex(QERROR, QUEUE_FULL, "Circular Buffer Queue is full");
throw ex;
}
for(queueElems = 0; queueElems < MAX_QUEUE_ELEMENTS; queueElems++)
{
if(m_QueueStructure[queueElems].inUse == false)
break;
}
boost::shared_array<char> tData(new char[bufferSize]);
m_QueueStructure[queueElems].data = tData;
m_QueueStructure[queueElems].inUse = true;
m_QueueStructure[queueElems].compressedLength = _compressedLength;
m_QueueStructure[queueElems].uncompressedLength = _uncompressedLength;
m_QueueStructure[queueElems].packetType = _packetType;
m_CurrentElementsOfQueue++;
return queueElems;
}
Data& GetElement(int index)
{
Data& DataElement = m_QueueStructure[index];
return DataElement;
}
void ClearElementIndex(Data& delValue)
{
m_CurrentElementsOfQueue--;
delValue.inUse = false;
}
};
for(queueElems = 0; queueElems < MAX_QUEUE_ELEMENTS; queueElems++) after looping queueElems has value 32 but in your m_QueueStructure only 32 elements so you trying to access m_QueueStructure[queueElems].data to 33rd element. That the problem.
EDIT: try use m_QueueStructure[queueElems].data.reset(new char[bufferSize]);
Solved the problem. Two changes I did. In the wait_and_pop function, I was returning an index rather than a Data&. When I returned Data&, that solved the assignment problem. Another crash was happening due to a memset of a shared_array.get(). Lesson learnt, never memset a shared_array or a shared_ptr.