Count Complete Tree Nodes
Total Accepted: 28036 Total Submissions: 115325 Difficulty: Medium
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.
思路
programcreek
Steps to solve this problem:
1) get the height of left-most part
2) get the height of right-most part
3) when they are equal, the # of nodes = 2^h -1
4) when they are not equal, recursively get # of nodes from left&right sub-trees
public class Solution {
public int countNodes(TreeNode root) {
if(root==null)
return 0;
int left = getLeftHeight(root)+1;
int right = getRightHeight(root)+1;
if(left==right){
return (2<<(left-1))-1;
}else{
return countNodes(root.left)+countNodes(root.right)+1;
}
}
public int getLeftHeight(TreeNode n){
if(n==null) return 0;
int height=0;
while(n.left!=null){
height++;
n = n.left;
}
return height;
}
public int getRightHeight(TreeNode n){
if(n==null) return 0;
int height=0;
while(n.right!=null){
height++;
n = n.right;
}
return height;
}
}