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  • Kth Smallest Element in a BST

    Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.

    Note: 
    You may assume k is always valid, 1 ≤ k ≤ BST's total elements.

    Follow up:
    What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?

     1 /**
     2  * Definition for a binary tree node.
     3  * struct TreeNode {
     4  *     int val;
     5  *     TreeNode *left;
     6  *     TreeNode *right;
     7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     8  * };
     9  */
    10 class Solution {
    11 public:
    12     int kthSmallest(TreeNode* root, int k) {
    13         stack <TreeNode*> tmp_s;
    14         TreeNode* tmp=root;
    15         while(tmp!=NULL){
    16             tmp_s.push(tmp);
    17             tmp=tmp->left;
    18         }
    19         while(k>0&&(tmp!=NULL||!tmp_s.empty())){
    20             if(tmp==NULL){
    21                 tmp=tmp_s.top();
    22                 tmp_s.pop();
    23                 if(--k==0)
    24                     return tmp->val;
    25                 tmp=tmp->right;
    26             }
    27             else{
    28                 while(tmp!=NULL){
    29                     tmp_s.push(tmp);
    30                     tmp=tmp->left;
    31                 }
    32             }
    33         }
    34         return tmp->val;
    35     }
    36 };
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  • 原文地址:https://www.cnblogs.com/zl1991/p/4670114.html
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