《劍指offer》——二叉樹的深度

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
        val(x), left(NULL), right(NULL) {}
};

int TreeDepth(TreeNode* pRoot)
{
    if(pRoot == NULL)
        return 0;
    int dLeft = TreeDepth(pRoot -> left);
    int dRight = TreeDepth(pRoot -> right);
    return(dLeft < dRight) ? (dRight + 1) : (dLeft + 1);
}