食物链(Food Chain) 题解

思路分析

按题目要求使用对应数据结构与算法模拟/递推求解，注意数据范围边界与时间复杂度。

参考代码

#include <iostream>
#include <vector>
#include <numeric>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, k;
    if (!(cin >> n >> k)) return 0;
    vector<int> p(n + 1), d(n + 1, 0);
    iota(p.begin(), p.end(), 0);
    auto find = [&](auto& self, int x) -> int {
        if (p[x] == x) return x;
        int r = self(self, p[x]);
        d[x] = (d[x] + d[p[x]]) % 3;
        return p[x] = r;
    };
    int fake = 0;
    for (int i = 0; i < k; ++i) {
        int t, x, y;
        cin >> t >> x >> y;
        if (x > n || y > n || (t == 2 && x == y)) {
            ++fake;
            continue;
        }
        int rel = (t == 1) ? 0 : 1;
        int rx = find(find, x), ry = find(find, y);
        if (rx == ry) {
            if ((d[x] - d[y] + 3) % 3 != rel) ++fake;
        } else {
            p[rx] = ry;
            d[rx] = (d[y] - d[x] + rel + 6) % 3;
        }
    }
    cout << fake << "\n";
    return 0;
}