hdu 1285 拓扑排序

简单的拓扑排序，要求字典序最小的话用优先队列来维护入度为0的点即可。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;

const int N = 501;
const int M = 10000;
int head[N];
int ans[N];
int in[N];
int n, m, e;

struct Edge 
{
    int v, next;
} edge[M];

void addEdge( int u, int v )
{
    edge[e].v = v;
    edge[e].next = head[u];
    head[u] = e++;
}

void topo()
{
    priority_queue<int, vector<int>, greater<int> > q;
    for ( int i = 1; i <= n; i++ )
    {
        if ( !in[i] ) q.push(i);
    }
    int cnt = 0;
    while ( !q.empty() )
    {
        int u = q.top();
        q.pop();
        printf("%d", u);
        cnt++;
        if ( cnt != n ) putchar(' ');
        else putchar('
');
        for ( int i = head[u]; i != -1; i = edge[i].next )
        {
            int v = edge[i].v;
            in[v]--;
            if ( in[v] == 0 )
            {
                q.push(v);
            }
        }
    }
}

int main ()
{
    while ( scanf("%d%d", &n, &m) != EOF )
    {
        e = 0;
        memset( head, -1, sizeof(head) );
        memset( in, 0, sizeof(in) );
        while ( m-- )
        {
            int u, v;
            scanf("%d%d", &u, &v);
            addEdge( u, v );
            in[v]++;
        }
        topo();
    }
    return 0;
}