L15_isBalancedJava

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