LeetCode-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.

    public boolean isBalanced(TreeNode root) {
        if (root == null) return true;
        if (Math.abs(maxDepth(root.left)-maxDepth(root.right)) > 1) return false;
        return isBalanced(root.left) && isBalanced(root.right);
    }
    
    private int maxDepth(TreeNode root) {
        if (root == null) return 0;
        return Math.max(maxDepth(root.left), maxDepth(root.right))+1;
    }

    public boolean isBalanced(TreeNode root) {
        if (root == null) return true;
        if (depth(root) == -1) return false;
        return true;
    }
    
    private int depth(TreeNode root) {
        if (root == null) return 0;
        int left = depth(root.left);
        int right = depth(root.right);
        if (left == -1 || right == -1) return -1;
        if (Math.abs(left-right) > 1) return -1;
        return Math.max(left, right)+1;
    }

其实，树的这种递推性质，如果可以自下向上都是对之前算法的一个很好的优化！！！多感悟此类问题。

LeetCode-Balanced Binary Tree

原文：http://blog.csdn.net/my_jobs/article/details/47663845