hdu 5154 Harry and Magical Computer

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題目連結：http://acm.hdu.edu.cn/showproblem.php?pid=5154

題意分析：有向圖問題，要求判斷是否存在環。 發現並查集竟然也能處理有向圖問題~~

/*Harry and Magical ComputerTime Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 1028    Accepted Submission(s): 415Problem DescriptionIn reward of being yearly outstanding magic student, Harry gets a magical computer. When the computer begins to deal with a process, it will work until the ending of the processes. One day the computer got n processes to deal with. We number the processes from 1 to n. However there are some dependencies between some processes. When there exists a dependencies (a, b), it means process b must be finished before process a. By knowing all the m dependencies, Harry wants to know if the computer can finish all the n processes. InputThere are several test cases, you should process to the end of file.For each test case, there are two numbers n m on the first line, indicates the number processes and the number of dependencies. 1≤n≤100,1≤m≤10000The next following m lines, each line contains two numbers a b, indicates a dependencies (a, b). 1≤a,b≤n OutputOutput one line for each test case. If the computer can finish all the process print "YES" (Without quotes).Else print "NO" (Without quotes). Sample Input3 23 12 13 33 22 11 3 Sample OutputYESNO SourceBestCoder Round #25 */#include <cstdio>#include <cstring>const int maxn = 1000 + 10;int n, m, p[maxn];int find(int x, int y){    if(p[y] == x) return 1;    if(p[y] == y) return 0;    find(x, p[y]);}int main(){    int a, b;    while(~scanf("%d%d", &n, &m)){        int flag = 0;        for(int i = 1; i <= n; i++) p[i] = i;        for(int i = 0; i < m; i++){            scanf("%d%d", &a, &b);            if(find(a, b)) flag = 1;            else p[a] = b;        }         if(!flag) printf("YES\n");        else printf("NO\n");     }    return 0;}

 

hdu 5154 Harry and Magical Computer