Leetcod刷题（15）—— 110. 平衡二叉树

  3
   / \
  9  20
    /  \
   15   7

 1
      / \
     2   2
    / \
   3   3
  / \
 4   4

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isBalanced(TreeNode root) {
        if(root==null){
            return true;
        }
        if(Math.abs(getDepth(root.left)-getDepth(root.right))<=1){
            return isBalanced(root.left)&&isBalanced(root.right);
        }
        return false;
    }
    
    public int getDepth(TreeNode root){
        if(root ==null){
            return 0;
        }
        if(root.left==null&&root.right==null){
            return 1;
        }
        return Math.max(getDepth(root.left),getDepth(root.right))+1;
    }
}

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
      public boolean isBalanced(TreeNode root) {
        
        height(root);
        return ans;
    }
    
    boolean ans = true;
    
    int height(TreeNode root)
    {
        if(root == null)
            return 0;
        int leftHeight = height(root.left);
        int rightHeight = height(root.right);
        if(Math.abs(leftHeight-rightHeight)>1){
            ans = false;
        }
        return Math.max(leftHeight,rightHeight)+1;
    }
}