700. Search in a Binary Search Tree

找到以val为根的子树 

#include <iostream>
#include <algorithm>
#include "vector"
#include "string"
#include "set"
#include "queue"
using namespace std;

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


TreeNode* searchBST(TreeNode* root, int val) 
{
	TreeNode* node = root;
	if (node == NULL)
	{
		return NULL;
	}
	if (node->val == val)
	{
		return node;
	}
	else if (node->val > val)
	{
		return searchBST(node->left, val);
	}
      //else if(node->val < val)!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
	else 
	{
		return searchBST(node->right, val);
	}
}

int main()
{
	
		TreeNode *n1 = new TreeNode(0);
		TreeNode *n2 = new TreeNode(0);
		TreeNode *n3 = new TreeNode(0);
		TreeNode *n4 = new TreeNode(0);
		TreeNode *n5 = new TreeNode(0);
		n1->val = 4; n1->left = n2; n1->right = n3;
		n2->val = 2; n2->left = n4; n2->right =n5;
		n3->val = 7; n3->left = NULL; n3->right = NULL;
		n4->val = 1; n4->left = NULL; n3->right = NULL;
		n5->val = 3; n5->left = NULL; n5->right = NULL;
	
		searchBST(n1, 2);

	system("pause");
	return 0;
}