Day 58

题目描述

思路

直接采取中序遍历，不过我们将k参与到中序遍历中，遍历到第k个元素就结束

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    int x=1;
    int num;
    public void mid(TreeNode root,int k){
        if(root==null||x>k){
            return;
        }
        mid(root.left,k);
        if(x==k){
            num=root.val;
        }
        x++;
        mid(root.right,k);
    }
    public int kthSmallest(TreeNode root, int k) {
        mid(root,k);
        return num;
    }
}