题解 | 小红的三带一

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

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    
    int ans = 0;
    for (int i = 0; i + 3 < n; ) {
        int x1 = a[i], x2 = a[i+1], x3 = a[i+2], x4 = a[i+3];
        
        vector<int> tmp = {x1, x2, x3, x4};
        sort(tmp.begin(), tmp.end());
  
        if ((tmp[0] == tmp[2] && tmp[3] != tmp[0]) || 
            (tmp[1] == tmp[3] && tmp[0] != tmp[1])) {
            ans++;
            i += 4;  
        } else {
            i++;  
        }
    }
    
    cout << ans << endl;
    return 0;
}