Broken backspace

#include <bits/stdc++.h>

using namespace std;

int edit(string X, string Y) {

    size_t n = X.size();
    size_t m = Y.size();

    vector<vector<int>> distance(n+1, vector<int>(m+1));

    distance[0][0] = 0;

    for (size_t i = 1; i <= n; i++)
        distance[i][0] = i;
    
    for (size_t j = 1; j <= m; j++)
        distance[0][j] = j;
    
    for (size_t i = 1; i <= n; i++) {
        for (size_t j = 1; j <= m; j++) {

            //int a = 1 + distance[i-1][j];
            int b = 1 + distance[i][j-1];
            //int c = ((X[n-i] == Y[m-j]) ? 0 : 1) + distance[i-1][j-1];

            if (X[n-i] == Y[m-j]) {
                distance[i][j] = min(distance[i-1][j-1], b);
            } else {
                distance[i][j] = b;
            }

            //distance[i][j] = min(a, min(b, c));

        }
    }

    return distance[n][m];

}

int main() {

    string s, t;
    cin >> s >> t;

    int sn = s.size(), tn = t.size();

    if (tn > sn) {
        cout << "No" << endl;
        return 0;
    } else if (tn == sn) {
        if (s == t) cout << "Yes" << endl;
        else cout << "No" << endl;
        return 0;
    }

    unordered_map<char, int> s_char_occurences;
    for (int c : s) {
        if (s_char_occurences.count(c)) {
            s_char_occurences[c] = 1;
        } else {
            s_char_occurences[c]++;
        }
    }

    unordered_map<char, int> t_char_occurences;
    for (int c : t) {
        if (t_char_occurences.count(c)) {
            t_char_occurences[c] = 1;
            if (!s_char_occurences.count(c)) {
                cout << "No" << endl;
                return 0;
            }
        } else {
            t_char_occurences[c]++;
            if (t_char_occurences[c] > s_char_occurences[c]) {
                cout << "No" << endl;
                return 0;
            }
        }
    }

    int n = edit(t, s);
    if (n == sn - tn) {
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED

Test 31

Verdict: ACCEPTED

Test 32

Verdict: ACCEPTED

Test 33

Verdict: ACCEPTED

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED

Test 36

Verdict: ACCEPTED

Test 37

Verdict: ACCEPTED

Test 38

Verdict: ACCEPTED

Test 39

Verdict: ACCEPTED

Test 40

Verdict: ACCEPTED

Test 41

Verdict: ACCEPTED

Test 42

Verdict: ACCEPTED

Test 43

Verdict: ACCEPTED

Test 44

Verdict: ACCEPTED

Test 45

Verdict: ACCEPTED

Test 46

Verdict: ACCEPTED

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: RUNTIME ERROR

Test 51

Verdict: RUNTIME ERROR

Test 52

Verdict: RUNTIME ERROR

Test 53

Verdict: RUNTIME ERROR

Test 54

Verdict: RUNTIME ERROR

Test 55

Verdict: RUNTIME ERROR

Test 56

Verdict: RUNTIME ERROR

Test 57

Verdict: ACCEPTED

Test 58

Verdict: RUNTIME ERROR