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; }