考研算法

题目

题目链接

题目要求

输出拓扑序列

代码

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 100010, M = 100010;

int n, m;
struct Node
{
    int id;
    Node* next;
    Node(int _id): id(_id), next(NULL) {}
}*head[N];
int d[N], q[N];

void add(int a, int b)
{
    auto p = new Node(b);
    p->next = head[a];
    head[a] = p;
}

bool topsort()
{
    int hh = 0, tt = -1;
    for (int i = 1; i <= n; i ++ )
        if (!d[i])
            q[ ++ tt] = i;

    while (hh <= tt)
    {
        int t = q[hh ++ ];
        for (auto p = head[t]; p; p = p->next)
            if ( -- d[p->id] == 0)
                q[ ++ tt] = p->id;
    }

    return tt == n - 1;
}

int main()
{
    scanf("%d%d", &n, &m);
    while (m -- )
    {
        int a, b;
        scanf("%d%d", &a, &b);
        d[b] ++ ;
        add(a, b);
    }

    if (!topsort()) puts("-1");
    else
    {
        for (int i = 0; i < n; i ++ )
            printf("%d ", q[i]);
    }

    return 0;
}

知识点

先占一个位置，明天再来补，今天没时间做了，也看得不太好