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  1. #include <bits/stdc++.h>
  2. #define ll long long
  3. #define el '\n'
  4. #define sandra ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  5. using namespace std;
  6.  
  7. ll count_swaps(const string &s, char start) {
  8.     ll mismatch = 0;
  9.     for (ll i = 0; i < s.size(); i++) {
  10.         char expected = (i % 2 == 0) ? start : (start == '0' ? '1' : '0');
  11.         if (s[i] != expected) mismatch++;
  12.     }
  13.     return mismatch / 2;
  14. }
  15.  
  16. signed main() {
  17.     sandra
  18.  
  19.     ll t = 0;
  20.     cin >> t;
  21.     while (t--) {
  22.         ll num;
  23.         string s;
  24.         cin >> num >> s;
  25.  
  26.         int zeros = count(s.begin(), s.end(), '0');
  27.         int ones = num - zeros;
  28.  
  29.         if (abs(zeros - ones) > 1) {
  30.             cout << -1 << el;
  31.         } else {
  32.             ll ans = LLONG_MAX;
  33.             if (zeros >= ones)
  34.                 ans = min(ans, count_swaps(s, '0'));
  35.             if (ones >= zeros)
  36.                 ans = min(ans, count_swaps(s, '1'));
  37.             cout << ans << el;
  38.         }
  39.     }
  40.     return 0;
  41. }
  42.  
Success #stdin #stdout 0.01s 5312KB
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https://ideone.com/Y9vE3H
language:
C++ (gcc 8.3)
created:
5 days ago
visibility:
public

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