题解 | #交叉线#

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

int main() {
    int T = 0;
    cin >> T;
    while(T--){
        int n = 0;
        cin >> n;
        vector<int> num(n);
        for(int i = 0; i < n; i++){
            cin >> num[i];
        }

        vector<vector<int>> circle(n-1, vector<int>(2));
        for(int i = 0; i < n - 1; i++){
            circle[i][0] = min(num[i], num[i + 1]);
            circle[i][1] = max(num[i], num[i + 1]);
        }
        int flag = 0;
        for(int i = 0; i < n - 1; i++){
            for(int j = 0; j < i; j++){
                if((circle[i][0] < circle[j][0] && circle[i][1] > circle[j][0] && circle[i][1] < circle[j][1]) || (circle[i][0] > circle[j][0] && circle[i][0] < circle[j][1] && circle[i][1] > circle[j][1])){
                    flag = 1;
                    break;
                }

                if(flag) break;
            }
        }

        if(flag) cout << "y" <<endl;
        else cout << "n" << endl;


    }
    return 0;
}
// 64 位输出请用 printf("%lld")