Inversions

#include <iostream>
#include <cmath>
#include <algorithm>
#include <bitset>
#include <vector>

using namespace std;

typedef long long ll;




int main() {

  string s;
  cin >> s;

  vector<bool> b;
  for (auto c : s) {
    b.push_back(c=='1');
  }

  int n = b.size();
  
  ll codd = 0;
  ll ceven = 0;
  for (int i=0; i<n; i++) {
    codd += b[i]^(i&1);
    ceven += !(b[i]^(i&1));
  }
  
  cout << min(codd, ceven) << endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED