总是 WA on 15，自己没有看出来错误。

代码：

#include <bits/stdc++.h>
using namespace std;
mt19937 rnd(time(0));

int n, k, d(1), u;
vector<int> vec;

bool ask(int x, int y, int c){  // c 是否在 (x,y) 上
    cout << "? " << x << ' ' << c << ' ' << y << endl;
    string s;
    cin >> s;
    return s == "Yes";
}

signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> k;
    for (int s(1); s<n; ++d) s += s*k;

    for (int i(1); i<=30; ++i){
        int x(rnd()%n+1), y(rnd()%n+1);
        while (y == x) y = rnd()%n+1;
        vec.clear();
        for (int j(1); j<=n; ++j){
            if (j != x && j != y && ask(x, y, j)) vec.push_back(j);
        }
        if (vec.size() == (d<<1)-3){
            u = x;
            break;
        }
    }

    for (auto i: vec){
        int cnt(0);
        for (auto j: vec){
            if (i == j) continue;
            cnt += ask(u, i, j);
        }
        if (cnt == d-2){
            cout << "! " << i << endl;
            return 0;
        }
    }

    return 0;
}