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.

BalancedTree.java

public boolean isBalanced(TreeNode root) {
    return getHeight(root) >= 0;
}

private int getHeight(TreeNode root) {
    if(root == null)
        return 0;

    int leftHeight = getHeight(root.left);
    if(leftHeight < 0)
        return -1;
    int rightHeight = getHeight(root.right);
    if(rightHeight < 0)
        return -1;

    if(Math.abs(leftHeight - rightHeight) > 1)
        return -1;

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