题目描述

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样例

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算法1

(暴力枚举) $O(n^2)$

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时间复杂度

参考文献

C++ 代码

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算法2

(暴力枚举) $O(n^2)$

blablabla

时间复杂度

参考文献

C++ 代码

#include<iostream>
#include<queue>
#include<cstring>

using namespace std;
typedef pair<int, int> PII;

const int N = 10010, M = 20010;
int n, m;
int h[N], e[M], ne[M], idx;
int din[N];
int dist[N];
int cnt;


void topsort()
{
    for (int i = 1; i <= n; i ++) dist[i] = 100;
    queue<PII> q;

    for (int i = 1; i <= n; i ++) 
        if (!din[i])
            q.push({100, i});

    while(q.size())
    {
        auto t = q.front();
        q.pop();
        cnt ++;
        for (int i = h[t.second]; ~i; i = ne[i])
        {
            int j = e[i];
            dist[j] = max(dist[j], t.first + 1);
            if (-- din[j] == 0)
                q.push({dist[j], j});
        }
    }
}

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}

int main()
{
    cin >> n >> m;
    memset(h, -1, sizeof h);
    while(m --)
    {
        int a, b;
        cin >> a >> b;
        add(b, a);
        din[a] ++;
    }

    topsort();a
    if (cnt < n) puts("Poor Xed");
    else
    {
        int res = 0;
        for (int i = 1; i <= n; i ++) res += dist[i];
        cout << res;
    }
    return 0;

}