该函数需要传入某已知节点、该节点的depth/level和目标节点，将返回目标节点的depth/level
目标节点在已知节点的子树中才可以，通常传入整个树，如下

	level = Rec_GetLevel(t, 1, target);

#include <stdio.h>
#include <stdlib.h>
#define NOT_FOUND -999
typedef struct node{int Element;struct node* Left;struct node* Right;
}Node;int Rec_GetLevel(Node* base_node, int base_level, Node* target)
{if (base_node == NULL)return NOT_FOUND;if (target == base_node)return base_level;int level_from_left, level_from_right;level_from_left = Rec_GetLevel(base_node->Left, base_level + 1, target);if (level_from_left != NOT_FOUND)return level_from_left;level_from_right = Rec_GetLevel(base_node->Right, base_level + 1, target);if (level_from_right != NOT_FOUND)return level_from_right;return NOT_FOUND;
}