双指针找子字符串位置

#include <iostream>

using namespace std;

int main() {
    string s, s1, s2, st;
    getline(cin, st);
    int l = 0, r;
    for (int i = 0; st[i]; i++) {
        if (st[i] == ',' && l == 0) l = i;
        else if (st[i] == ',' && l != 0) r = i;
    }
    s = st.substr(0, l);
    s1 = st.substr(l + 1, r - l - 1);
    s2 = st.substr(r + 1,st.size() - r - 1);
    //cout << s << ' ' << s1 << ' ' << s2;

    int m = -1, n = -1;

    for (int i = 0; i < s.size(); i++ ) {
        int j = 0;
        int k = i;
        while (s[k] == s1[j] && j < s1.size()) {
            k++;
            j++;
        }
        if (j == s1.size()){
           m = k - 1;
           break; 
        } 
    }

    for (int i = s.size() - 1;i > 0; i--) {
        int j = s2.size() - 1;
        int k = i;
        while (s[k] == s2[j] && j >= 0) {
            k--;
            j--;
        }
        if (j == -1) {
            n = k + 1;
            break;
        }
    }

    if (m == -1 || n == -1 || (n - m < 0)) cout << "-1" << endl;
    else cout << n - m - 1 << endl;
    return 0;

}