merge sorted array elements not printing - visual-c++

Question

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
void merge(vector<int>& nums1, int n, vector<int>& nums2, int m) {
int i = n - 1, j = m - 1, k = n + m - 1;
while (i >= 0 && j >= 0) {
if (nums1[i] < nums2[j]) {
nums1[k--] = nums2[j--];
} else {
nums1[k--] = nums1[i--];
}
}
while (j >= 0) {
nums1[k--] = nums2[j--];
}
for (int i = 0; i < nums1.size(); i++) {
cout << nums1[i] << " ";
}
}
int main() {
vector<int> i = { 1, 3, 5, 7 };
vector<int> j = { 0, 2, 4, 6, 8, 10 };
int n = i.size();
int m = j.size();
merge(i, n, j, m);
return 0;
}
I want to print the merged sorted array now, but its always printing unmerged array(ie: the array before merging)
I tried many solutions and in one its just giving unsorted garbage kind of values.

Answer 1

C++ vectors, unlike javascript arrays, are not automatically resized upon storing elements at index values greater or equal to the allocated length. The behavior is undefined and could cause a segmentation fault or other program failures.
You must resize nums1 using the resize method before storing the merged values from the end of the combined length.
Note also that you should use type size_t for the index and length variables, which is tricky as you cannot rely on negative values to detect end conditions. Careful implementation actually results in simpler code as shown below.
Here is a modified version:
#include <iostream>
#include <vector>
using namespace std;
void merge(vector<int>& nums1, size_t n, vector<int>& nums2, size_t m) {
size_t i = n, j = m, k = n + m;
if (nums1.size() < k) {
nums1.resize(k);
}
while (i > 0 && j > 0) {
if (nums1[i - 1] < nums2[j - 1]) {
nums1[--k] = nums2[--j];
} else {
nums1[--k] = nums1[--i];
}
}
while (j > 0) {
nums1[--k] = nums2[--j];
}
}
int main() {
vector<int> a = { 1, 3, 5, 7 };
vector<int> b = { 0, 2, 4, 6, 8, 10 };
merge(a, a.size(), b, b.size());
for (size_t i = 0; i < a.size(); i++) {
cout << a[i] << " ";
}
cout << endl;
return 0;
}