110. Balanced Binary Tree

110. Balanced Binary Tree

判断树是不是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.

My Solutions:

1。不用global variable

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

2。用global variable

private boolean result = true;

public boolean isBalanced(TreeNode root) {
    maxDepth(root);
    return result;
}

public int maxDepth(TreeNode root) {
    if (root == null) return 0;
    int l = maxDepth(root.left);
    int r = maxDepth(root.right);

    if (Math.abs(l - r) > 1) result = false;
    return 1 + Math.max(l, r);
}