lintcode93- Balanced Binary Tree- easy

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.

Example

Given binary tree A = {3,9,20,#,#,15,7}, B = {3,#,20,15,7}

A)  3            B)    3 
   / \                  \
  9  20                 20
    /  \                / \
   15   7              15  7

The binary tree A is a height-balanced binary tree, but B is not.

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1. 分治+遍历，用全局变量。注意一下根据定义，空树null也是一颗平衡二叉树。

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param root: The root of binary tree.
     * @return: True if this Binary tree is Balanced, or false.
     */
    
    private boolean isBalanceTree;
    
    public boolean isBalanced(TreeNode root) {
        // write your code here
        
        isBalanceTree = true;
        height(root);
        return isBalanceTree;
    }
    
    private 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) {
            isBalanceTree = false;
        }
        
        return Math.max(leftHeight, rightHeight) + 1;
    }
}

---

 

2.分治，不用全局变量用ResultType。

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param root: The root of binary tree.
     * @return: True if this Binary tree is Balanced, or false.
     */
    
    private class ResultType{
        public int height;
        public boolean isBalanceTree;
        
        public ResultType(int height, boolean isBalanceTree) {
            this.height = height;
            this.isBalanceTree = isBalanceTree;
        }
    }
    
    public boolean isBalanced(TreeNode root) {
        // write your code here
        ResultType result = helper(root);
        return result.isBalanceTree;
    }
    
    private ResultType helper(TreeNode root) {
        
        ResultType result = new ResultType(0, true);
        
        if (root == null) {
            return result;
        }
        
        ResultType left = helper(root.left);
        ResultType right = helper(root.right);
        
        if (!left.isBalanceTree || !right.isBalanceTree ||
        Math.abs(left.height - right.height) > 1) {
            result.isBalanceTree = false;
        }
        result.height = Math.max(left.height, right.height) + 1;
        
        return result;
    }
}