hdu 3342 Legal or Not

原题链接：http://acm.hdu.edu.cn/showproblem.php?pid=3342
拓扑排序。。

#include<algorithm>#include<iostream>#include<cstdlib>#include<cstring>#include<cstdio>#include<vector>#include<queue>#include<map>using std::cin;using std::cout;using std::endl;using std::find;using std::sort;using std::map;using std::pair;using std::queue;using std::vector;using std::multimap;#define pb(e) push_back(e)#define sz(c) (int)(c).size()#define mp(a, b) make_pair(a, b)#define all(c) (c).begin(), (c).end()#define iter(c) decltype((c).begin())#define cls(arr,val) memset(arr,val,sizeof(arr))#define cpresent(c, e) (find(all(c), (e)) != (c).end())#define rep(i, n) for (int i = 0; i < (int)(n); i++)#define tr(c, i) for (iter(c) i = (c).begin(); i != (c).end(); ++i)const int N = 10010;typedef unsigned long long ull;struct Node { int to, next; };struct TopSort {    Node G[N];    int tot, topNum, inq[N], head[N];    inline void init() {        tot =  topNum = 0;        cls(inq, 0), cls(head, -1);    }    inline void add_edge(int u, int v) {        G[tot].to = v; G[tot].next = head[u]; head[u] = tot++;    }    inline void built(int m) {        int u, v;        rep(i, m) {            scanf("%d %d", &u, &v);            inq[v]++;            add_edge(u, v);        }    }    inline void bfs(int n) {        queue<int> q;        rep(i, n) { if (!inq[i]) q.push(i); }        while (!q.empty()) {            int u = q.front(); q.pop();            topNum++;            for (int i = head[u]; ~i; i = G[i].next) {                if (--inq[G[i].to] == 0) q.push(G[i].to);            }        }        puts(topNum == n ? "YES" : "NO");    }}work;int main() {#ifdef LOCAL    freopen("in.txt", "r", stdin);    freopen("out.txt", "w+", stdout);#endif    int n, m;    while (~scanf("%d %d", &n, &m), n + m) {        work.init();        work.built(m);        work.bfs(n);    }    return 0;}