USACO 2022 US Open Contest Bronze Division - Photoshoot

Problem link: here

Solution Author: Stefan Dascalescu

Problem Solution

We only care about substrings of length two with different characters and do a bit of casework there.

Source codes

The source codes in C++ and Python can be seen below.

#include <bits/stdc++.h>
using namespace std;

int main() 
{
    int n;
    cin >> n;

    string s;
    cin >> s;

    int cnt = 0;
    for(int i = n-1; i >= 0; i -= 2)
        if(s[i] != s[i-1] && (cnt + s[i]) % 2 == 0)
            cnt++;

    cout << cnt;
    return 0;
}

n = int(input())
s = input().strip()
cnt = 0
for i in range(n - 1, 0, -2):
    if s[i] != s[i - 1] and (cnt + ord(s[i])) % 2 == 0:
        cnt += 1
print(cnt)