[Swust OJ 856]--Huge Tree(并查集)

题目链接：http://acm.swust.edu.cn/problem/856/

Time limit(ms): 1000　　　　　　　　Memory limit(kb): 10000

Description

　　There are N trees in a forest. At first, each tree contains only one node as its root. And each node is marked with a number.

　　You're asked to do the following two operations:

　　A X Y, you need to link X's root to Y as a direct child. If X and Y have already been in the same tree, ignore this operation.

　　B X, you need to output the maximum mark in the chain from X to its root (inclusively).

Input

　　The first line contains an integer T, indicating the number of followed cases. (1 <= T <= 20)

　　For each case, the first line contains two integers N and M, indicating the number of trees at beginning, and the number of operations follows,　　respectively. (1 <= N, M <= 100,000)

　　And the following line contains N integers, which are the marks of the N trees. (0 <= Mark <= 100,000)

　　And the rest lines contain the operations, in format A X Y, or B X, (0 <= X, Y < N).

Output

　　For each 'B X' operation, output the maximum mark.

Sample Input

　　

1 5 5 5 4 2 9 1 A 1 2 A 0 4 B 4 A 1 0 B 1

Sample Output

　　

1 5

题目大意：就是一个数组（下标从零开始），有对应的A,B操作，A a,b,是把a所在集合归并到b上，

若某一个集合已合并不进行操作，然B a,就是查询a集合中的最大值。

解题思路：运用并查集就是，注意a集合到b所在集合，并查集合并区分一下就可以了

代码如下：

 #include <stdio.h>
 int n, m, maxn, t, f[], cur[];

 void init(){
     scanf("%d%d", &n, &m);
     for (int i = ; i <= n; i++){
         scanf("%d", &cur[i]);
         f[i] = i;
     }
 }

 int findset(int x){
     maxn = cur[x];
     if (f[x] == x) return x;
     int y = findset(f[x]);
     if (maxn > cur[x]) cur[x] = maxn;
     else maxn = cur[x];
     return f[x] = y;
 }

 void mergy(){
     int i, x, y;
     char k[];
     for (i = ; i < m; i++){
         scanf("%s", k);
         if (k[] == 'A'){
             scanf("%d%d", &x, &y);
             int a = findset(x), b = findset(y);
             if (a != b) f[a] = y;//注意和传统并查集的区别
         }
         else{
             scanf("%d", &x);
             findset(x);
             printf("%d\n", cur[x]);
         }
     }
 }

 int main(){
     scanf("%d", &t);
     while (t--){
         init();
         mergy();
     }
     return ;
 }