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  • Balanced Binary Tree

    Given a binary tree, determine if it is height-balanced.

    For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

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

    Better Solution (CTCI)

    /**
     * Definition for binary tree
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution {
        public boolean isBalanced(TreeNode root) {
            if(checkHeight(root) == -1)
                return false;
            else
                return true;
        }
        
        private int checkHeight(TreeNode root){
            if(root == null)
                return 0;
            
            int leftHeight = checkHeight(root.left);
            if(leftHeight == -1)
                return -1;
            
            int rightHeight = checkHeight(root.right);
            if(rightHeight == -1)
                return -1;
            
            if(Math.abs(leftHeight - rightHeight) > 1)
                return -1;
            else
                return Math.max(leftHeight, rightHeight)+1;
        }
    }
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  • 原文地址:https://www.cnblogs.com/RazerLu/p/3533077.html
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