Make string S equal to T after replacing some prefix characters in S

#include <bits/stdc++.h>

using namespace std;

int solve(string s, string t)

{

    int n = s.size();

    string ss = s, tt = t;

    sort(ss.begin(), ss.end()), sort(tt.begin(), tt.end());

    if (ss != tt) {

        return -1;

    }

    int ans = n;

    int left = 0, right = n - 1;

    reverse(t.begin(), t.end());

    while (left < right) {

        int mid = (left + right) / 2;

        int cur = n - 1;

        for (auto ch : t) {

            if (cur == mid - 1)

                break;

            if (ch == s[cur]) {

                --cur;

            }

        }

        if (cur == mid - 1) {

            right = mid;

            ans = right;

        }

        else {

            left = mid + 1;

        }

    }

    return ans;

}

int main()

{

    string s = "abab";

    string t = "abba";

    cout << solve(s, t);

    return 0;

}

#include <bits/stdc++.h>

using namespace std;

int solve(string s, string t)

{

    int n = s.size();

    string ss = s, tt = t;

    sort(ss.begin(), ss.end()), sort(tt.begin(), tt.end());

    if (ss != tt) {

        return -1;

    }

    int ans = n;

    int left = 0, right = n - 1;

    reverse(t.begin(), t.end());

    while (left < right) {

        int mid = (left + right) / 2;

        int cur = n - 1;

        for (auto ch : t) {

            if (cur == mid - 1)

                break;

            if (ch == s[cur]) {

                --cur;

            }

        }

        if (cur == mid - 1) {

            right = mid;

            ans = right;

        }

        else {

            left = mid + 1;

        }

    }

    return ans;

}

int main()

{

    string s = "abab";

    string t = "abba";

    cout << solve(s, t);

    return 0;

}