国产操作系统生态圈推动信息安全与技术自主发展的新机遇
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2022-10-03
POJ 3321 Apple Tree (树状数组)
Description
Input
The first line contains an integer N (N ≤ 100,000) , which is the number of the forks in the tree.The following N - 1 lines each contain two integers u and v, which means fork u and fork v are connected by a branch.The next line contains an integer M (M ≤ 100,000).The following M lines each contain a message which is either“C x” which means the existence of the apple on fork x has been changed. i.e. if there is an apple on the fork, then Kaka pick it; otherwise a new apple has grown on the empty fork.or“Q x” which means an inquiry for the number of apples in the sub-tree above the fork x, including the apple (if exists) on the fork xNote the tree is full of apples at the beginning
Output
For every inquiry, output the correspond answer per line.
Sample Input
31 21 33Q 1C 2Q 1
Sample Output
32
题意
给出一棵苹果树,每个节点一开始都有苹果。
C X :如果 X 点有苹果,则拿掉,如果没有,则新长出一个。
Q X :查询 X 点与它的所有后代分支一共有几个苹果。
思路
通过一次 dfs 记录每个节点的 dfs 序 num[i] 以及其所有后代 dfs 序中的最大值 son[i] 。
我们按照 dfs 序将每个节点维护在数组中,则节点 a 的所有后代分支部分即 num[i] 与 son[i] 之间的部分。
于是问题便变成了区间点修改以及查询了,用线段树或者树状数组都可以解决。
AC 代码
#include
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