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  • LeetCode Trim a Binary Search Tree

    原题链接在这里:https://leetcode.com/problems/trim-a-binary-search-tree/description/

    题目:

    Given a binary search tree and the lowest and highest boundaries as L and R, trim the tree so that all its elements lies in [L, R] (R >= L). You might need to change the root of the tree, so the result should return the new root of the trimmed binary search tree.

    Example 1:

    Input: 
        1
       / 
      0   2
    
      L = 1
      R = 2
    
    Output: 
        1
          
           2

    Example 2:

    Input: 
        3
       / 
      0   4
       
        2
       /
      1
    
      L = 1
      R = 3
    
    Output: 
          3
         / 
       2   
      /
     1

    题解:

    在[L, R]区间外trim. 

    Recursive call, stop condition, root == null, return root.

    如果root.val 小于 L, 则root右侧有可能在区间内,返回trim后的 root.right. 

    如果root.val 大于 R, 则root左侧有可能在区间内,返回trim后的root.left.

    如果root.val在区间内, 则对左右两侧分别trim后return root.

    Time Complexity: O(n), n 是node数.

    Space: O(logn), stack space.

    AC Java:

     1 /**
     2  * Definition for a binary tree node.
     3  * public class TreeNode {
     4  *     int val;
     5  *     TreeNode left;
     6  *     TreeNode right;
     7  *     TreeNode(int x) { val = x; }
     8  * }
     9  */
    10 class Solution {
    11     public TreeNode trimBST(TreeNode root, int L, int R) {
    12         if(root == null){
    13             return root;
    14         }
    15         
    16         if(root.val < L){
    17             return trimBST(root.right, L, R);
    18         }
    19         if(root.val > R){
    20             return trimBST(root.left, L, R);
    21         }
    22         
    23         root.left = trimBST(root.left, L, R);
    24         root.right = trimBST(root.right, L, R);
    25         
    26         return root;
    27     }
    28 }
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  • 原文地址:https://www.cnblogs.com/Dylan-Java-NYC/p/7513171.html
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