[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：

 1 #include <stdio.h>

 2 int n, m, maxn, t, f[100005], cur[100005];

 3 

 4 void init(){

 5     scanf("%d%d", &n, &m);

 6     for (int i = 0; i <= n; i++){

 7         scanf("%d", &cur[i]);

 8         f[i] = i;

 9     }

10 }

11 

12 int findset(int x){

13     maxn = cur[x];

14     if (f[x] == x) return x;

15     int y = findset(f[x]);

16     if (maxn > cur[x]) cur[x] = maxn;

17     else maxn = cur[x];

18     return f[x] = y;

19 }

20 

21 void mergy(){

22     int i, x, y;

23     char k[3];

24     for (i = 0; i < m; i++){

25         scanf("%s", k);

26         if (k[0] == 'A'){

27             scanf("%d%d", &x, &y);

28             int a = findset(x), b = findset(y);

29             if (a != b) f[a] = y;//注意和传统并查集的区别

30         }

31         else{

32             scanf("%d", &x);

33             findset(x);

34             printf("%d\n", cur[x]);

35         }

36     }

37 }

38 

39 int main(){

40     scanf("%d", &t);

41     while (t--){

42         init();

43         mergy();

44     }

45     return 0;

46 }

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