题目链接：http://hihocoder.com/problemset/problem/1174
题意：判断一个有向图是否有环，用拓扑排序，结论就是每次取出点的时候统计一下现在剩下几个点，最后没有剩下点就是无环的。
1 /* 2 ━━━━━┒ギリギリ♂ eye！ 3 ┓┏┓┏┓┃キリキリ♂ mind！ 4 ┛┗┛┗┛┃＼○／ 5 ┓┏┓┏┓┃ / 6 ┛┗┛┗┛┃ノ) 7 ┓┏┓┏┓┃ 8 ┛┗┛┗┛┃ 9 ┓┏┓┏┓┃ 10 ┛┗┛┗┛┃ 11 ┓┏┓┏┓┃ 12 ┛┗┛┗┛┃ 13 ┓┏┓┏┓┃ 14 ┃┃┃┃┃┃ 15 ┻┻┻┻┻┻ 16 */ 17 #include <algorithm> 18 #include <iostream> 19 #include <iomanip> 20 #include <cstring> 21 #include <climits> 22 #include <complex> 23 #include <fstream> 24 #include <cassert> 25 #include <cstdio> 26 #include <bitset> 27 #include <vector> 28 #include <deque> 29 #include <queue> 30 #include <stack> 31 #include <ctime> 32 #include <set> 33 #include <map> 34 #include <cmath> 35 using namespace std; 36 #define fr first 37 #define sc second 38 #define cl clear 39 #define BUG puts("here!!!") 40 #define W(a) while(a--) 41 #define pb(a) push_back(a) 42 #define Rint(a) scanf("%d", &a) 43 #define Rll(a) scanf("%lld", &a) 44 #define Rs(a) scanf("%s", a) 45 #define Cin(a) cin >> a 46 #define FRead() freopen("in", "r", stdin) 47 #define FWrite() freopen("out", "w", stdout) 48 #define Rep(i, len) for(int i = 0; i < (len); i++) 49 #define For(i, a, len) for(int i = (a); i < (len); i++) 50 #define Cls(a) memset((a), 0, sizeof(a)) 51 #define Clr(a, x) memset((a), (x), sizeof(a)) 52 #define Full(a) memset((a), 0x7f7f7f, sizeof(a)) 53 #define lrt rt << 1 54 #define rrt rt << 1 | 1 55 #define pi 3.14159265359 56 #define RT return 57 #define lowbit(x) x & (-x) 58 #define onenum(x) __builtin_popcount(x) 59 typedef long long LL; 60 typedef long double LD; 61 typedef unsigned long long ULL; 62 typedef pair<int, int> pii; 63 typedef pair<string, int> psi; 64 typedef pair<LL, LL> pll; 65 typedef map<string, int> msi; 66 typedef vector<int> vi; 67 typedef vector<LL> vl; 68 typedef vector<vl> vvl; 69 typedef vector<bool> vb; 70 71 const int maxn = 100100; 72 const int maxm = 500500; 73 typedef struct Edge { 74 int u, v; 75 int next; 76 }Edge; 77 Edge edge[maxm]; 78 int ecnt, head[maxn]; 79 int n, m; 80 int dig[maxn]; 81 priority_queue<int, vector<int>, greater<int> > pq; 82 83 void adde(int u, int v) { 84 edge[ecnt].u = u; 85 edge[ecnt].v = v; 86 edge[ecnt].next = head[u]; 87 head[u] = ecnt++; 88 } 89 90 int main() { 91 // FRead(); 92 int T, u, v; 93 Rint(T); 94 W(T) { 95 ecnt = 0; Clr(head, -1); Cls(dig); 96 Rint(n); Rint(m); 97 Rep(i, m) { 98 Rint(u); Rint(v); 99 adde(u, v); 100 dig[v]++; 101 } 102 while(!pq.empty()) pq.pop(); 103 For(i, 1, n+1) if(dig[i] == 0) pq.push(i); 104 int cnt = n; 105 while(!pq.empty()) { 106 u = pq.top(); pq.pop(); 107 cnt--; 108 for(int i = head[u]; ~i; i=edge[i].next) { 109 v = edge[i].v; 110 if(--dig[v] == 0) pq.push(v); 111 } 112 } 113 if(cnt != 0) printf("Wrong "); 114 else printf("Correct "); 115 } 116 RT 0; 117 }