判断二叉树是否是平衡二叉树

题目描述：输入一棵二叉树，判断该二叉树是否是平衡二叉树

function TreeNode(x) {
    this.val = x
    this.left = null
    this.right = null
}

function IsBalanced_Solution(pRoot) {
    if(!pRoot) return true
    var llen = treeDepth(pRoot.left),
        rlen = treeDepth(pRoot.right)
    if(Math.abs(llen - rlen) > 1) return false
    return IsBalanced_Solution(pRoot.left) && IsBalanced_Solution(pRoot.right)
}

function treeDepth(p) {
     if(!p) return 0
     if(!p.left && !p.right) return 1
     return Math.max(treeDepth(p.left), treeDepth(p.right)) + 1
}