題目描述

/*思路：根據二叉搜尋樹的特點，中序遍歷的數值是遞增排序的，因此，只需中序遍歷二叉搜尋樹就能找到第k大結點*/
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
	TreeNode* KthNode(TreeNode* pRoot, int k)
	{
		if (pRoot == NULL || k <= 0)
			return NULL;
		return kthnode(pRoot, k);
	}
	TreeNode* kthnode(TreeNode* pRoot, int& k)          //中序遍歷查詢第k個結點
	{
		TreeNode* target = NULL;
		if (pRoot->left != NULL)
			target  = kthnode(pRoot->left, k);
		if (target == NULL)
		{
			if (k == 1)
				target = pRoot;
			--k;
		}
		if (pRoot->right&&target == NULL)
			target = kthnode(pRoot->right, k);
		return target;
	}
};