110. Balanced Binary Tree.md

#110. 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.

思路：寻找每个节点的子树的高度，也就是需要一个获取树高度的方法。这里可以遍历的时候顺便计数，当差值大于1的时候就直接跳出循环，减少不必要的运算。

    //求root节点的高度的方法，其高度等于左子树与右子树较高者+1
     int height(TreeNode *root){
        if (root == NULL)return 0;
        int lh = height(root->left);
        int rh = height(root->right);
        if (lh > rh)return lh + 1;
        else return rh + 1;
    }

Java Solution

public class Solution {
    public boolean isBalanced(TreeNode root) {
        return getBalancedHeight(root)!=-1;
    }
    public int getBalancedHeight(TreeNode root){
        if(root==null) return 0;
        int leftH = getBalancedHeight(root.left);
        if(leftH<0)return -1;
        int rightH= getBalancedHeight(root.right);
        if(rightH<0)return -1;
        if(Math.abs(leftH-rightH)>1)return -1;
        return Math.max(leftH,rightH)+1;
    }
}