func TreeDepth( pRoot *TreeNode ) int {
    // write code here
    var a,b int
    if pRoot==nil {
        return 0
    }
    a = TreeDepth(pRoot.Left)
    b = TreeDepth(pRoot.Right)
    return Max(a,b)+1
}

func Max(a,b int) int {
    if a > b {
        return a
    } else {
        return b
    }
}