Balanced Binary Tree

Source

LintCode 93

LeetCode 110

Problem

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.

Example

Given binary tree A={3,9,20,#,#,15,7}, B={3,#,20,15,7}

A)  3            B)    3 
   / \                  \
  9  20                 20
    /  \                / \
   15   7              15  7

The binary tree A is a height-balanced binary tree, but B is not.

Solution

public boolean isBalanced(TreeNode root) {
    int height = heightOfTree(root);
    return height != -1;
}

public int heightOfTree(TreeNode root) {
    if (root == null ) return 0;

    int leftHeight = heightOfTree(root.left);
    int rightHeight = heightOfTree(root.right);
    if (leftHeight == -1 || rightHeight == -1) {
        return -1;
    }
    if (Math.abs(leftHeight - rightHeight) > 1) return -1;

    return Math.max(leftHeight, rightHeight) + 1;
}