CSU 1004 Xi and Bo

1004: Xi and Bo

Time Limit: 1 Sec   Memory Limit: 128 MB
Submit: 479   Solved: 177
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Description

Bo has been in Changsha for four years. However he spends most of his time staying his small dormitory. One day he decides to get out of the dormitory and see the beautiful city. So he asks to Xi to know whether he can get to another bus station from a bus station. Xi is not a good man   because he doesn’t tell Bo directly. He tells to Bo about some buses’ routes. Now Bo turns to you and he hopes you to tell him whether he can get to another bus station from a bus station directly according to the Xi’s information.

Input

The first line of the input contains a single integer T (0<T<30) which is the number of test cases. For each test case, the first contains two different numbers representing the starting station and the ending station that Bo asks. The second line is the number n (0<n<=50) of buses’ routes which Xi tells. For each of the following n lines, the first number m (2<=m<= 100) which stands for the number of bus station in the bus’ route. The remaining m numbers represents the m bus station. All of the bus stations are represented by a number, which is between 0 and 100.So you can think that there are only 100 bus stations in Changsha.

Output

For each test case, output the “Yes” if Bo can get to the ending station from the starting station by taking some of buses which Xi tells. Otherwise output “No”. One line per each case. Quotes should not be included.

Sample Input

30 333 1 2 33 4 5 63 1 5 60 423 0 2 32 2 43 214 2 1 0 3

Sample Output

NoYesYes

HINT

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并查集，两个月前做这道题的时候，没过，甚至想用BFS写，现在写了并查集，一遍过。

题目大概是说 给出一些公交车的路线，问从给出的起点能否走到终点。

方法：并查集。把公交车路线上的点合并为一个集合，最后查询起点和终点是否在同一个集合。

#include <stdio.h>
#define N 105
int fa[N];
int a[N];
void InitSet(int n){
    for(int i=1; i<=n; i++) fa[i] = i ;
}
int Find(int x) {
    return fa[x] == x ? x : fa[x] = Find(fa[x]) ;
}
bool Merge(int u ,int v) {
    int fu = Find(u) , fv = Find(v) ;
    if(fu != fv) fa[fv] = fu ;
    return fu != fv ;
}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        InitSet(100);
        int kstart,kend;
        scanf("%d%d",&kstart,&kend);
        int n;
        scanf("%d",&n);
        while(n--)
        {
            int m;
            scanf("%d",&m);
            for(int i=0;i<m;i++)
                scanf("%d",&a[i]);
            for(int i=1;i<m;i++)
                Merge(a[i-1],a[i]);
        }
        printf("%s\n",Find(kstart)==Find(kend)?"Yes":"No");
    }
    return 0;
}