平衡二叉树

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

public boolean IsBalanced_Solution(TreeNode root) {
    return Height(root) != -1;
}

public int Height(TreeNode node) {
    if (node == null) {
        return 0;
    }
    int leftDepth = Height(node.left);
    if (leftDepth == -1) {
        return -1;
    }
    
    int rightDepth = Height(node.right);
    if (rightDepth == -1) {
        return -1;
    }
    
    if (Math.abs(leftDepth - rightDepth) > 1) {
        return -1;
    }
    
    return Math.max(leftDepth, rightDepth) + 1;
}