标签：ssi bin etl pes div target href val 复杂度
题目：
Given a complete binary tree, count the number of nodes.
Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
题意及分析：给出一颗完全二叉树，要求二叉树的节点数。完全二叉树的定义为：叶节点只能出现在最下层和次下层，并且最下面一层的结点都集中在该层最左边的若干位置的二叉树。直接遍历统计会超时。 如果从某节点一直向左的高度 = 一直向右的高度, 那么以该节点为root的子树一定是complete binary tree. 而 complete binary tree的节点数,可以用公式算出 2^h - 1. 如果高度不相等, 则递归调用 return countNode(left) + countNode(right) + 1. 复杂度为O(h^2) \
代码：
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public int countNodes(TreeNode root) { if(root==null) return 0; int left=getLeft(root)+1; int right = getRight(root)+1; if(left==right) return (2<<(left-1))-1; else{ return countNodes(root.left)+countNodes(root.right)+1; } } public int getLeft(TreeNode node){ int count = 0; while(node.left!=null){ node=node.left; count++; } return count; } public int getRight(TreeNode node){ int count = 0; while (node.right!=null){ node=node.right; count++; } return count; } }
[LeetCode] 222. Count Complete Tree Nodes Java
标签：ssi bin etl pes div target href val 复杂度
原文地址：http://www.cnblogs.com/271934Liao/p/7231077.html
