110. Balanced Binary Tree

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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

Solution 1

2ms 22.81% Recursively check the left depth and right depth of a node, absolutely not the best solution.

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

Solution2 Improvement on the solution 1

This method should be faster than the first one but I don't know why it cost more time.

21ms 3.83%

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

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