https://leetcode.com/problems/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.
Example 1:
Input: root = [3,1,4,null,2], k = 1 3 / 1 4 2 Output: 1
Example 2:
Input: root = [5,3,6,2,4,null,null,1], k = 3 5 / 3 6 / 2 4 / 1 Output: 3
代码:
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ #include <iostream> using namespace std; class Solution { public: int kthSmallest(TreeNode* root, int k) { if(!root) return 0; vector<int> ans; pre(root, ans); sort(ans.begin(), ans.end()); if(k > ans.size()) return 0; else return ans[k - 1]; } void pre(TreeNode* root, vector<int>& ans) { if(root) { ans.push_back(root -> val); if(root -> left != NULL) pre(root -> left, ans); if(root -> right != NULL) pre(root -> right, ans); } } };