I need to write logic to break down a 4 digit number into individual digits.
On a reply here at SO to a question regarding 3 digits, someone gave the math below:
int first = 321/100;
int second = (321/10)-first*10;
int third = (321/1)-first*100-second*10;
Can someone help me?
Thank you in advance!
Well, using the sample you found, we can quite easily infer a code for you.
The first line says int first = 321/100;, which returns 3 (integer division is the euclidian one). 3 is indeed the first integer in 321 so that's a good thing. However, we have a 4 digit number, let's try replacing 100 with 1000:
int first = 4321/1000;
This does return 4 !
Let's try adapting the rest of your code (plus I put your four digit number in the variable entry).
int entry = 4321;
int first = entry/1000;
int second = entry/100 - first*10;
int third = entry/10 - first*100 - second*10;
int fourth = entry - first*1000 - second*100 - third*10;
second will be entry/100 (43) minus first*10 (40), so we're okay.
third is then 432 - 400 - 30 which turns to 2. This also works till fourth.
For more-than-four digits, you may want to use a for-loop and maybe some modulos though.
This snip of code counts the number of digits input from the user
then breaks down the digits one by one:
PRINT "Enter value";
INPUT V#
X# = V#
DO
IF V# < 1 THEN
EXIT DO
END IF
D = D + 1
V# = INT(V#) / 10
LOOP
PRINT "Digits:"; D
FOR L = D - 1 TO 0 STEP -1
M = INT(X# / 10 ^ L)
PRINT M;
X# = X# - M * 10 ^ L
NEXT
END
Related
I tried to make a Python program that removes specific digit from a number, example a = 12025 k = 2 result is 105, however none of the guides helped me do that, can anybody help me with that?
Conversion to string does not seem elegant.
As pseudo-code:
number without digit (number, digit)
if number == digit
0
else if number < 10
number
else if number % 10 == digit
number without digit (number / 10, digit)
else
number without digit (number / 10, digit) * 10 + (number % 10)
Where / is integer division, truncating the remainder, and % is the modulo, remainder.
So it is a matter of recursion.
You have to convert into str type, then remove the occurrencies, and go back to int
int(str(a).replace(str(k),''))
a = 12025
k = 2
print(int(str(a).replace(str(k), '')))
If you want to use math rather than converting to and from string you can do
a = 12025
k = 2
result = 0
exp = 0
while a:
a, remainder = divmod(a, 10)
if remainder != k:
result = result + 10**exp * remainder
exp += 1
I am trying to convert a string of varchar to ascii. Then i'm trying to make it so any number that's not 3 digits has a 0 in front of it. then i'm trying to add a 1 to the very beginning of the string and then i'm trying to make it a large number that I can apply math to it.
I've tried a lot of different coding techniques. The closest I've gotten is below:
s = 'Ak'
for c in s:
mgk = (''.join(str(ord(c)) for c in s))
num = [mgk]
var = 1
num.insert(0, var)
mgc = lambda num: int(''.join(str(i) for i in num))
num = mgc(num)
print(num)
With this code I get the output: 165107
It's almost doing exactly what I need to do but it's taking out the 0 from the ord(A) which is 65. I want it to be 165. everything else seems to be working great. I'm using '%03d'% to insert the 0.
How I want it to work is:
Get the ord() value from a string of numbers and letters.
if the ord() value is less than 100 (ex: A = 65, add a 0 to make it a 3 digit number)
take the ord() values and combine them into 1 number. 0 needs to stay in from of 65. then add a one to the list. so basically the output will look like:
1065107
I want to make sure I can take that number and apply math to it.
I have this code too:
s = 'Ak'
for c in s:
s = ord(c)
s = '%03d'%s
mgk = (''.join(str(s)))
s = [mgk]
var = 1
s.insert(0, var)
mgc = lambda s: int(''.join(str(i) for i in s))
s = mgc(s)
print(s)
but then it counts each letter as its own element and it will not combine them and I only want the one in front of the very first number.
When the number is converted to an integer, it
Is this what you want? I am kinda confused:
a = 'Ak'
result = '1' + ''.join(str(f'{ord(char):03d}') for char in a)
print(result) # 1065107
# to make it a number just do:
my_int = int(result)
I encountered an interview question:
Given a input String: aaaaabcddddee, convert it to a5b1c1d4e2.
One extra constraint is, this needs to be done in-place, means no extra space(array) should be used.
It is guaranteed that the encoded string will always fit in the original string. In other words, string like abcde will not occur, since it will be encoded to a1b1c1d1e1 which occupies more space than the original string.
One hint interviewer gave me was to traverse the string once and find the space that is saved.
Still I am stuck as some times, without using extra variables, some values in the input string may be overwritten.
Any suggestions will be appreciated?
This is a good interview question.
Key Points
There are 2 key points:
Single character must be encoded as c1;
The encoded length will always be smaller than the original array.
Since 1, we know each character requires at least 2 places to be encoded. This is to say, only single character will require more spaces to be encoded.
Simple Approach
From the key points, we notice that the single character causes us a lot problem during the encoding, because they might not have enough place to hold the encoded string. So how about we leave them first, and compressed the other characters first?
For example, we encode aaaaabcddddee from the back while leaving the single character first, we will get:
aaaaabcddddee
_____a5bcd4e2
Then we could safely start from the beginning and encoding the partly encoded sequence, given the key point 2 such that there will be enough spaces.
Analysis
Seems like we've got a solution, are we done? No. Consider this string:
aaa3dd11ee4ff666
The problem doesn't limit the range of characters, so we could use digit as well. In this case, if we still use the same approach, we will get this:
aaa3dd11ee4ff666
__a33d212e24f263
Ok, now tell me, how do you distinguish the run-length from those numbers in the original string?
Well, we need to try something else.
Let's define Encode Benefit (E) as: the length difference between the encoded sequence and the original consecutive character sequence..
For example, aa has E = 0, since aa will be encoded to a2, and they have no length difference; aaa has E = 1, since it will be encoded as a3, and the length difference between the encoded and the original is 1. Let's look at the single character case, what's its E? Yes, it's -1. From the definition, we could deduce the formula for E: E = ori_len - encoded_len.
Now let's go back to the problem. From key point 2, we know the encoded string will always be shorter than the original one. How do we use E to rephrase this key point?
Very simple: sigma(E_i) >= 0, where E_i is the Encode Benefit of the ith consecutive character substring.
For example, the sample you gave in your problem: aaaaabcddddee, can be broken down into 5 parts:
E(0) = 5 - 2 = 3 // aaaaa -> a5
E(1) = 1 - 2 = -1 // b -> b1
E(2) = 1 - 2 = -1 // c -> c1
E(3) = 4 - 2 = 2 // dddd -> d4
E(4) = 2 - 2 = 0 // ee -> e2
And the sigma will be: 3 + (-1) + (-1) + 2 + 0 = 3 > 0. This means there will be 3 spaces left after encoding.
However, from this example, we could see a potential problem: since we are doing summing, even if the final answer is bigger than 0, it's possible to get some negatives in the middle!
Yes, this is a problem, and it's quite serious. If we get E falls below 0, this means we do not have enough space to encode the current character and will overwrite some characters after it.
But but but, why do we need to sum it from the first group? Why can't we start summing from somewhere in the middle to skip the negative part? Let's look at an example:
2 0 -1 -1 -1 1 3 -1
If we sum up from the beginning, we will fall below 0 after adding the third -1 at index 4 (0-based); if we sum up from index 5, loop back to index 0 when we reach the end, we have no problem.
Algorithm
The analysis gives us an insight on the algorithm:
Start from the beginning, calculate E of the current consecutive group, and add to the total E_total;
If E_total is still non-negative (>= 0), we are fine and we could safely proceed to the next group;
If the E_total falls below 0, we need to start over from the current position, i.e. clear E_total and proceed to the next position.
If we reach the end of the sequence and E_total is still non-negative, the last starting point is a good start! This step takes O(n) time. Usually we need to loop back and check again, but since key point 2, we will definitely have a valid answer, so we could safely stop here.
Then we could go back to the starting point and start traditional run-length encoding, after we reach the end we need to go back to the beginning of the sequence to finish the first part. The tricky part is, we need to make use the remaining spaces at the end of the string. After that, we need to do some shifting just in case we have some order issues, and remove any extra white spaces, then we are finally done :)
Therefore, we have a solution (the code is just a pseudo and hasn't been verified):
// find the position first
i = j = E_total = pos = 0;
while (i < s.length) {
while (s[i] == s[j]) j ++;
E_total += calculate_encode_benefit(i, j);
if (E_total < 0) {
E_total = 0;
pos = j;
}
i = j;
}
// do run length encoding as usual:
// start from pos, end with len(s) - 1, the first available place is pos
int last_available_pos = runlength(s, pos, len(s)-1, pos);
// a tricky part here is to make use of the remaining spaces from the end!!!
int fin_pos = runlength(s, 0, pos-1, last_available_pos);
// eliminate the white
eliminate(s, fin_pos, pos);
// update last_available_pos because of elimination
last_available_pos -= pos - fin_pos < 0 ? 0 : pos - fin_pos;
// rotate back
rotate(s, last_available_pos);
Complexity
We have 4 parts in the algorithm:
Find the starting place: O(n)
Run-Length-Encoding on the whole string: O(n)
White space elimination: O(n)
In place string rotation: O(n)
Therefore we have O(n) in total.
Visualization
Suppose we need to encode this string: abccdddefggggghhhhh
First step, we need to find the starting position:
Group 1: a -> E_total += -1 -> E_total = -1 < 0 -> E_total = 0, pos = 1;
Group 2: b -> E_total += -1 -> E_total = -1 < 0 -> E_total = 0, pos = 2;
Group 3: cc -> E_total += 0 -> E_total = 0 >= 0 -> proceed;
Group 4: ddd -> E_total += 1 -> E_total = 1 >= 0 -> proceed;
Group 5: e -> E_total += -1 -> E_total = 0 >= 0 -> proceed;
Group 6: f -> E_total += -1 -> E_total = -1 < 0 -> E_total = 0, pos = 9;
Group 7: ggggg -> E_total += 3 -> E_total = 3 >= 0 -> proceed;
Group 8: hhhhh -> E_total += 3 -> E_total = 6 >= 0 -> end;
So the start position will be 9:
v this is the starting point
abccdddefggggghhhhh
abccdddefg5h5______
^ last_available_pos, we need to make use of these remaining spaces
abccdddefg5h5a1b1c2
d3e1f1___g5h5a1b1c2
^^^ remove the white space
d3e1f1g5h5a1b1c2
^ last_available_pos, rotate
a1b1c2d3e1f1g5h5
Last Words
This question is not trivial, and actually glued several traditional coding interview questions together naturally. A suggested mind flow would be:
observe the pattern and figure out the key points;
realize the reason for insufficient space is because of encoding single character;
quantize the benefit/cost of encoding on each consecutive characters group (a.k.a Encoding Benefit);
use the quantization you proposed to explain the original statement;
figure out the algorithm to find a good starting point;
figure out how to do run-length-encoding with a good starting point;
realize you need to rotate the encoded string and eliminate the white spaces;
figure out the algorithm to do in place string rotation;
figure out the algorithm to do in place white space elimination.
To be honest, it's a bit challenging for an interviewee to come up with a solid algorithm in a short time, so your analysis flow really matters. Don't say nothing, show your mind flow, this helps the interviewer to find out your current stage.
Maybe just encode it normally, but if you see that your output index overtakes the input index, just skip the "1". Then when you finish go backwards and insert 1 after all letters without a count, shifting the rest of the string back. It is O(N^2) in the worst case (no repeating letters), so I assume there might be better solutions.
EDIT: it appears I missed the part that the final string always fits into the source. With that restriction, yeah, this is not the optimal solution.
EDIT2: an O(N) version of it would be during the first pass also compute the final compressed length (which in the general case might be more than the source), set pointer p1 to it, a pointer p2 to the compressed string with 1s omitted (p2 is thus <= p1), then just keep going backwards on both pointers, copying p2 to p1 and adding 1s when necessary (when this happens the difference between p2 and p1 will decrease)
O(n) and in place
set var = 0;
Loop from 1-length and find the first non-matching character.
The count would be the difference of the indices of both characters.
Let's run through an example
s = "wwwwaaadexxxxxxywww"
add a dummy letter to s
s = s + '#'
now our string becomes
s = "wwwwaaadexxxxxxywww#"
we'll come back to this step later.
j gives the first character of the string.
j = 0 // s[j] = w
now loop through 1 - length. The first non-matching character is 'a'
print(s[j], i - j) // i = 4, j = 0
j = i // j = 4, s[j] = a
Output: w4
i becomes the next non-matching character which would be 'd'
print(s[j], i - j) // i = 7, j = 4 => a3
j = i // j = 7, s[j] = d
Output: w4a3
.
. (Skipping to the second last)
.
j = 15, s[j] = y, i = 16, s[i] = w
print(s[j], i - y) => y1
Output: w4a3d1e1x6y1
Okay so now we reached the last, assume that we didn't add any dummy letter
j = 16, s[j] = w and we cannot print it's count
because we've no 'mis-matching' character
That's why need to add a dummy letter.
Here's a C++ implementation
void compress(string s){
int j = 0;
s = s + '#';
for(int i=1; i < s.length(); i++){
if(s[i] != s[j]){
cout << s[j] << i - j;
j = i;
}
}
}
int main(){
string s = "wwwwaaadexxxxxxywww";
compress(s);
return 0;
}
Output: w4a3d1e1x6y1w3
If the use of insert and erase string functions are allowed then you can efficiently get the solution with this implementation.
#include<bits/stdc++.h>
using namespace std;
int dig(int n){
int k=0;
while(n){
k++;
n/=10;
}
return k;
}
void stringEncoding(string &n){
int i=0;
for(int i=0;i<n.size();i++){
while(n[i]==n[i+j])j++;
n.erase((i+1),(j-1));
n.insert(i+1,to_string(j));
i+=(dig(j));
}
}
int main(){
ios_base::sync_with_stdio(0), cin.tie(0);
string n="kaaaabcddedddllllllllllllllllllllllp";
stringEncoding(n);
cout<<n;
}
This will give the following output : k1a4b1c1d2e1d3l22p1
I'm trying to get the first Digit of a Long but the Long i'm getting in from the user will be between 13 - 16 digits long how can I get that first Digit without knowing the exact length
Just format it into a character buffer and get the first one. Only if that becomes a performance bottleneck, come back for a more complex solution.
In Java:
// assuming the number is non-negative,
// otherwise need to deal with sign
String firstDigit = String.valueOf(myLong).substring(0,1);
You mentioned this is Java. In Java (and many C based languages), division of integers returns an integer and throws the remainder away. This means that while you have a multiple digit number (in other words, greater than 9), you can divide by 10 to remove the last digit. What you end up with is a single digit number that was the first digit of the original number:
if ( myLong < 0 ) {
myLong *= -1;
}
while ( myLong > 9 ) {
myLong /= 10;
}
The number of digits a number has is just (int)log_10(n). Therefore a power of 10 with the same number of digits as n is (int)pow(10, (int)log_10(n)).
The last digit therefore is just n / (int)pow(10, (int)log_10(n)).
In Java this translates to:
long n = 8797123456789L;
long numDigs = (long)Math.log10(n);
long lastDigit = n / (long)Math.pow(10, numDigs);
System.out.println(lastDigit);
>> 8
Consider the following function on a string:
int F(string S)
{
int N = S.size();
int T = 0;
for (int i = 0; i < N; i++)
for (int j = i + 1; j < N; j++)
if (S[i] > S[j])
T++;
return T;
}
A string S0 of length N with all pairwise distinct characters has a total of N! unique permutations.
For example "bac" has the following 6 permutations:
bac
abc
cba
bca
acb
cab
Consider these N! strings in lexicographical order:
abc
acb
bac
bca
cab
cba
Now consider the application of F to each of these strings:
F("abc") = 0
F("acb") = 1
F("bac") = 1
F("bca") = 2
F("cab") = 2
F("cba") = 3
Given some string S1 of this set of permutations, we want to find the next string S2 in the set, that has the following relationship to S1:
F(S2) == F(S1) + 1
For example if S1 == "acb" (F = 1) than S2 == "bca" (F = 1 + 1 = 2)
One way to do this would be to start at one past S1 and iterate through the list of permutations looking for F(S) = F(S1)+1. This is unfortunately O(N!).
By what O(N) function on S1 can we calculate S2 directly?
Suppose length of S1 is n, biggest value for F(S1) is n(n-1)/2, if F(S1) = n(n-1)/2, means it's a last function and there isn't any next for it, but if F(S1) < n(n-1)/2, means there is at least one char x which is bigger than char y and x is next to y, find such a x with lowest index, and change x and y places. let see it by example:
S1 == "acb" (F = 1) , 1 < 3 so there is a char x which is bigger than another char y and its index is bigger than y, here smallest index x is c, and by first try you will replace it with a (which is smaller than x so algorithm finishes here)==> S2= "cab", F(S2) = 2.
Now let test it with S2, cab: x=b, y=a, ==> S3 = "cba".\
finding x is not hard, iterate the input, and have a variable name it min, while current visited character is smaller than min, set min as newly visited char, and visit next character, first time you visit a character which is bigger than min stop iteration, this is x:
This is pseudocode in c# (but I wasn't careful about boundaries e.g in input.Substring):
string NextString(string input)
{
var min = input[0];
int i=1;
while (i < input.Length && input[i] < min)
{
min = input[i];
i++;
}
if (i == input.Length) return "There isn't next item";
var x = input[i], y=input[i-1];
return input.Substring(0,i-2) + x + y + input.Substring(i,input.Length - 1 - i);
}
Here's the outline of an algorithm for a solution to your problem.
I'll assume that you have a function to directly return the n-th permutation (given n) and its inverse, ie a function to return n given a permutation. Let these be perm(n) and perm'(n) respectively.
If I've figured it correctly, when you have a 4-letter string to permute the function F goes like this:
F("abcd") = 0
F("abdc") = 1
F(perm(3)) = 1
F(...) = 2
F(...) = 2
F(...) = 3
F(perm(7)) = 1
F(...) = 2
F(...) = 2
F(...) = 3
F(...) = 3
F(...) = 4
F(perm(13)) = 2
F(...) = 3
F(...) = 3
F(...) = 4
F(...) = 4
F(...) = 5
F(perm(19)) = 3
F(...) = 4
F(...) = 4
F(...) = 5
F(...) = 5
F(perm(24)) = 6
In words, when you go from 3 letters to 4 you get 4 copies of the table of values of F, adding (0,1,2,3) to the (1st,2nd,3rd,4th) copy respectively. In the 2nd case, for example, you already have one derangement by putting the 2nd letter in the 1st place; this simply gets added to the other derangements in the same pattern as would be true for the original 3-letter strings.
From this outline it shouldn't be too difficult (but I haven't got time right now) to write the function F. Strictly speaking the inverse of F isn't a function as it would be multi-valued, but given n, and F(n) there are only a few cases for finding m st F(m)==F(n)+1. These cases are:
n == N! where N is the number of letters in the string, there is no next permutation;
F(n+1) < F(n), the sought-for solution is perm(n+(N-1)!), ;
F(n+1) == F(n), the solution is perm(n+2);
F(n+1) > F(n), the solution is perm(n+1).
I suspect that some of this might only work for 4 letter strings, that some of these terms will have to be adjusted for K-letter permutations.
This is not O(n), but it is at least O(n²) (where n is the number of elements in the permutation, in your example 3).
First, notice that whenever you place a character in your string, you already know how much of an increase in F that's going to mean -- it's however many characters smaller than that one that haven't been added to the string yet.
This gives us another algorithm to calculate F(n):
used = set()
def get_inversions(S1):
inv = 0
for index, ch in enumerate(S1):
character = ord(ch)-ord('a')
cnt = sum(1 for x in range(character) if x not in used)
inv += cnt
used.add(character)
return inv
This is not much better than the original version, but it is useful when inverting F. You want to know the first string that is lexicographically smaller -- therefore, it makes sense to copy your original string and only change it whenever mandatory. When such changes are required, we should also change the string by the least amount possible.
To do so, let's use the information that the biggest value of F for a string with n letters is n(n-1)/2. Whenever the number of required inversions would be bigger than this amount if we didn't change the original string, this means we must swap a letter at that point. Code in Python:
used = set()
def get_inversions(S1):
inv = 0
for index, ch in enumerate(S1):
character = ord(ch)-ord('a')
cnt = sum(1 for x in range(character) if x not in used)
inv += cnt
used.add(character)
return inv
def f_recursive(n, S1, inv, ign):
if n == 0: return ""
delta = inv - (n-1)*(n-2)/2
if ign:
cnt = 0
ch = 0
else:
ch = ord(S1[len(S1)-n])-ord('a')
cnt = sum(1 for x in range(ch) if x not in used)
for letter in range(ch, len(S1)):
if letter not in used:
if cnt < delta:
cnt += 1
continue
used.add(letter)
if letter != ch: ign = True
return chr(letter+ord('a'))+f_recursive(n-1, S1, inv-cnt, ign)
def F_inv(S1):
used.clear()
inv = get_inversions(S1)
used.clear()
return f_recursive(len(S1), S1, inv+1, False)
print F_inv("acb")
It can also be made to run in O(n log n) by replacing the innermost loop with a data structure such as a binary indexed tree.
Did you try to swap two neighbor characters in the string? It seems that it can help to solve the problem. If you swap S[i] and S[j], where i < j and S[i] < S[j], then F(S) increases by one, because all other pairs of indices are not affected by this permutation.
If I'm not mistaken, F calculates the number of inversions of the permutation.