Hdu 3342 Legal or not（基于邻接表的BFS+队列的拓扑排序）

大意：拓扑排序或者Floyd判断是否有环。

 

基于邻接表的BFS实现的拓扑排序。

 

CODE1：

 

#include <iostream>
#include <queue>
using namespace std;
#define M 10005

struct edge
{
    int v, w, next;
}edge[20005];

int ind[M], first[M], cnt, n, m, tot, num;
int topo[M];

void init()
{
    cnt = 0;
    tot = 0;
    memset(first, -1, sizeof(first));
    memset(ind, 0, sizeof(ind));
    memset(topo, 0, sizeof(topo));
}

void read_graph(int u, int v)
{
    edge[cnt].v = v; edge[cnt].next = first[u]; first[u] = cnt++;
}

int toposort()
{
    queue<int> q;
    for(int u = 0; u < n; u++) if(!ind[u])    
    q.push(u);
    while(!q.empty())
    {
        int x = q.front();    q.pop();
        topo[++tot] = x;
        for(int e = first[x]; e != -1; e = edge[e].next)
        {
            if(--ind[edge[e].v] == 0)
            {
                q.push(edge[e].v);
            }
        }
    }
    if(tot != n) return 0;
        return 1;
}

int main()
{
    while(~scanf("%d%d", &n, &m), n, m)
    {
        init();
        while(m--)
        {
            int u, v;
            scanf("%d%d", &u, &v);
            read_graph(u, v);
            ind[v]++;
        }
        if(toposort())
        {
            printf("YES\n");
        }
        else    printf("NO\n");
    }
}

 

 CODE2：

 

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

const int M = 10005;
int u[4*M], v[4*M], next[4*M], w[4*M], topo[4*M];
int first[M], d[M];
int ind[M];
int n, m, cnt, tot;


void init()
{
    cnt = tot = 0;
    memset(ind, 0, sizeof(ind));
    memset(first, -1, sizeof(first));
    memset(next, 0, sizeof(next));
    memset(topo, 0, sizeof(topo));
    memset(d, 0, sizeof(d));
}

void read_graph(int u1, int v1)
{
    v[cnt] = v1, next[cnt] = first[u1], first[u1] = cnt++;
}

int toposort()
{
    queue<int> q;
    for(int i = 0; i < n; i++)    if(!ind[i])
        q.push(i);
    while(!q.empty())
    {
        int x = q.front(); q.pop();
        topo[++tot] = x;
        for(int e = first[x]; e!=-1; e = next[e])
        {
            if(--ind[v[e]] == 0)
            {
                q.push(v[e]);
            }
        }
    }
    if(tot != n) return 0;
        return 1;
}

int main()
{
    while(~scanf("%d%d", &n, &m), n, m)
    {
        init();
        while(m--)
        {
            int u1, v1;
            scanf("%d%d", &u1, &v1);
            read_graph(u1, v1);
            ind[v1]++;
        }
        if(toposort())
        {
            printf("YES\n");
        }
        else printf("NO\n");
    }
}