lightoj 1003

有向图拓扑排序，判段是否存在。

#include<map>
#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int MAXN = 20010;
struct Edge{
    int to, next;
};
Edge edge[MAXN >> 1];
int head[MAXN], ind[MAXN];
void addEdge(int u, int v, int k){
    edge[k].to = v;
    edge[k].next = head[u];
    head[u] = k;
}
int main(){
    int t, m, CASE(0);
    string str1, str2;
    //freopen("in.cpp", "r", stdin);
    scanf("%d", &t);
    while(t--){
        int NUM(0), cnt(0);
        map<string, int>mp;
        memset(ind, 0,  sizeof ind);
        memset(head, -1, sizeof head);
        scanf("%d", &m);
        for(int i = 0;i < m;i ++){
            int u, v;
            cin >> str1 >> str2;
            map<string, int>::iterator it = mp.find(str1);
            if(it == mp.end()) mp.insert(pair<string, int>(str1, ++NUM)), u = NUM;
            else u = it->second;
            it = mp.find(str2);
            if(it == mp.end()) mp.insert(pair<string, int>(str2, ++NUM)), v = NUM;
            else v = it->second;
            ind[u]++;
            addEdge(v, u, i+1);
        }
        while(cnt < NUM){
            int pos = 0;
            for(int i = 1;i <= NUM;i ++){
                if(ind[i] == 0){
                    cnt++;
                    ind[i]--;
                    pos = i;
                    break;
                }
            }
            if(!pos) break;
            for(int i = head[pos]; ~i; i = edge[i].next){
                int v = edge[i].to;
                ind[v]--;
            }
        }
        if(cnt == NUM) printf("Case %d: Yes\n", ++CASE);
        else printf("Case %d: No\n", ++CASE);
    }
    return 0;
}