Swapping letters

input/code.cpp: In function 'int main()':
input/code.cpp:33:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < letters.size(); i++) {
                    ~~^~~~~~~~~~~~~~~~
input/code.cpp:34:22: warning: array subscript has type 'char' [-Wchar-subscripts]
         at[letters[i]] = 0;
                      ^
input/code.cpp:35:23: warning: array subscript has type 'char' [-Wchar-subscripts]
         prx[letters[i]] = 0;
                       ^
input/code.cpp:36:23: warning: array subscript has type 'char' [-Wchar-subscripts]
         pvx[letters[i]] = 0;
                       ^
input/code.cpp:37:23: warning: array subscript has type 'char' [-Wchar-subscripts]
         pry[letters[i]] = 0;
                       ^
input/code.cpp:38:23: warning: array subscript has type 'char' [-Wchar-subscripts]
         pvy[letters[i]] = 0;
                       ^
input/code.cpp:51:14: warning: array subscript has type 'char' [-Wchar-subscr...

#include <vector>
#include <iostream>
#include <string>
 
std::vector<int> l0[1000];
int at[123];
int prx[123];
int pvx[123];
int pry[123];
int pvy[123];
 
std::string letters = "abcdefghijklmnopqrstuvwxyz";
 
int count(std::string s, char c, int a, int e) {
    int n = 0;
    for(int i = a; i < e; i++) {
        if (s.c_str()[i] == c) n++;
    }
    return n;
}
 
int find(std::string y, int a, char c) {
    int i = a;
    while(1) {
        if (y.c_str()[i] == c)
            break;
        i += 1;
    }
    return i;
}
 
int main() {
    for(int i = 0; i < letters.size(); i++) {
        at[letters[i]] = 0;
        prx[letters[i]] = 0;
        pvx[letters[i]] = 0;
        pry[letters[i]] = 0;
        pvy[letters[i]] = 0;
    }
 
    int n;
    std::cin >> n;
 
    while (n > 0) {
        n -= 1;
        char c0;
        char c1;
        std::cin >> c0;
        std::cin >> c1;
 
        l0[c0].push_back(c1);
        l0[c1].push_back(c0);
    }
 
    std::string x;
    std::string y;
 
    std::cin >> x;
    std::cin >> y;
 
    int i = 0;
    for(int i = 0; i < x.size(); i++) {
        //std::cout << i << " " << x.size() << std::endl;
        char c = x.c_str()[i];
        int j = find(y, at[c], c);
        at[c] = j + 1;
 
        for (int r : l0[c]) {
            /*
            int cx = count(x, r, pvx[c], i);
            pvx[c] = i + 1;
            prx[c] += cx;
            cx = prx[c];
            */
            int cx = prx[r];
 
            int cy = count(y, r, pvy[c], j);
            pvy[c] = j + 1;
            pry[c] += cy;
            cy = pry[c];
 
            if (cx != cy) {
                std::cout << "NO" << std::endl;
                return 0;
            }
        }
        prx[c] += 1;
    }
    std::cout << "YES" << std::endl;
    return 0;
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: ACCEPTED

Test 8

Verdict: TIME LIMIT EXCEEDED

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: TIME LIMIT EXCEEDED