HDU.3342 Legal or Not (拓扑排序 TopSort)

HDU.3342 Legal or Not (拓扑排序 TopSort)

题意分析

裸的拓扑排序 根据是否成环来判断是否合法

详解请移步

算法学习 拓扑排序（TopSort）

代码总览

#include <iostream>
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <sstream>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cmath>
#define nmax 200
#define MEM(x) memset(x,0,sizeof(x))
using namespace std;
int n,m;
int indegree[nmax];
vector<int> v[nmax];
bool suc = true;
void topsort()
{
    int cnt = 0;
    queue<int> q;
    while(1){
        for(int i = 0; i<n; ++i){
            if(indegree[i] == 0){
                q.push(i);
                cnt++;
                indegree[i] = -1;
            }
        }
        if(q.empty()) break;
        while(!q.empty()){
            int t = q.front();q.pop();
            for(int i = 0; i<v[t].size();++i){
                int tt = v[t][i];
                if(indegree[tt] == -1){
                    suc =false;
                    break;
                }else
                    indegree[tt]--;
            }
            if(!suc) break;
        }
        if(!suc) break;
    }
    if(suc && cnt!=n) suc = false;
}
int main()
{
    //freopen("in.txt","r",stdin);
    while(scanf("%d%d",&n,&m) == 2 && n){
        MEM(indegree);
        suc = true;
        for(int i = 0; i<n;++i) v[i].clear();
        for(int i = 0; i<m; ++i){
            int a,b;
            scanf("%d%d",&a,&b);
            indegree[b]++;
            v[a].push_back(b);
        }
        topsort();
        printf("%s\n",suc?"YES":"NO");
    }
    return 0;
}