二叉搜索树的第k个结点

题目描述

给定一颗二叉搜索树，请找出其中的第k大的结点。例如， 5 / \ 3 7 /\ /\ 2 4 6 8 中，按结点数值大小顺序第三个结点的值为4。

/*
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 || k ==0){
            return NULL;
        }
        //中序遍历
           stack<TreeNode*> stack;
        int index = 0;
          TreeNode *p = pRoot;        
        TreeNode *res = NULL;
        
        while(p || !stack.empty()){
            while(p){
                stack.push(p);
                p = p->left;
            }
            
            if(!stack.empty()){
                p = stack.top();
                stack.pop();
                index ++;
                if(index == k)
                {
                     res = p;
                    break;
                } 
                else p = p->right;
            }
        }
        
        return res;
        
    }

    
};