222. Count Complete Tree Nodes

/**
 * 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;
        //获取到左右两个深度
        int leftDepth=getLeftDepth(root)+1;
        int rightDepth=getRightDepth(root)+1;
        if(leftDepth==rightDepth)
        {
            
            //这里采用位运算可以让实际那复杂度更加低，如果调用pow计算的话，会超时
            return (2<<(leftDepth-1)) - 1;
            //return (int)Math.pow(2,leftDepth)-1;
        }
        else
        {
            return countNodes(root.left)+countNodes(root.right)+1;
        }
        
        
    }
    
    public int getLeftDepth(TreeNode root)
    {
        int res=0;
        TreeNode temp=root.left;
        while(temp!=null)
        {
            res++;
            temp=temp.left;
            
        }
        return res;
    }
    
    public int getRightDepth(TreeNode root)
    {
        int res=0;
        TreeNode temp=root.right;
        while(temp!=null)
        {
            res++;
            temp=temp.right;
        }
        return res;
        
    }
    
}