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.

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: Divide conquer

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