func_code_string: #include <bits/stdc++.h>   using namespace std;   int n;   char a[440000], b[440000];   int cnta = 0, cntb = 0;   int df[440000] = {0};   int czl[440000], czr[440000];   int zz1 = 0, zz2 = 0;   int ab[440000] = {0}, ba[440000] = {0};   int ans = 0;   int main() {     cin >> n;     cin >> a >> b;     for (int i = 0; i < n; i++) {       if (a[i] ==  a ) {         cnta++;         if (a[i] != b[i]) ab[++zz1] = i + 1;       }       if (b[i] ==  a ) {         cntb++;         if (a[i] != b[i]) ba[++zz2] = i + 1;       }     }     if ((zz1 + zz2) % 2 == 1) {       cout << -1 << endl;       return 0;     }     while (zz1 || zz2) {       if (zz2 % 2 == 1) {         zz2++;         ans++;         czl[ans] = ab[zz1], czr[ans] = ab[zz1];         ba[zz2] = ab[zz1];         zz1--;       }       if (zz1) {         ans++;         czl[ans] = ab[zz1], czr[ans] = ab[zz1 - 1];         zz1 -= 2;       } else {         ans++;         czl[ans] = ba[zz2], czr[ans] = ba[zz2 - 1];         zz2 -= 2;       }     }     cout << ans << endl;     for (int i = 1; i <= ans; i++) cout << czl[i] <<     << czr[i] << endl;     return 0;   }   