Longest Common Subsequence is not showing the result - c++

Question

I have written this code using dynamic programming approach and I think the logic is good but the code is not displaying the result. The code is as follows:
#include <iostream>
using namespace std;
void LCS(int input1[], int input2[], int n, int m) {
int L[n + 1][m + 1]; /*This matrix stores the length of common subsequences*/
for (int i = 0; i <= n; i++) {
for (int j = 0; j <= m; j++) {
if (i == 0 || j == 0)
L[i][j] = 0;
else if (input1[i - 1] == input2[j - 1])
L[i][j] = 1 + L[i - 1][j - 1];
else
L[i][j] = max(L[i - 1][j], L[i][j - 1]);
}
}
int index = L[n][m];
int lcs[index];
int i = n, j = m;
while (i > 0 && j > 0) {
if (input1[i - 1] == input2[j - 1]) {
lcs[index - 1] = input1[i - 1];
i--;
j--;
index--;
} else if (L[i - 1][j] > L[i][j - 1])
i--;
else
j--;
}
for (int i = 0; i < index; i++){
cout << lcs[i];
}
}
int main() {
int n, m;
cin >> n >> m;
int input1[n], input2[m]; /*two arrays from which longest subsequnce is to be found*/
for (int i = 0; i < n; i++)
cin >> input1[i];
for (int i = 0; i < m; i++)
cin >> input2[i];
LCS(input1, input2, n, m);
return 0;
}
The code terminates without showing any result!
I even switched to a different IDE but its the same. What is wrong with this?

Answer 1

You are modifying the index variable. Create a copy of it and modify that. Here I used temp.
int index = L[n][m];
int temp = index;
int lcs[index];
int i = n, j = m;
while (i > 0 && j > 0) {
if (input1[i - 1] == input2[j - 1]) {
lcs[temp - 1] = input1[i - 1];
i--;
j--;
temp--;
} else if (L[i - 1][j] > L[i][j - 1])
i--;
else
j--;
}
for (int i = 0; i < index; i++){
cout << lcs[i];
}
In your version index is decremented to zero when you want to print the result so nothing will be printed.