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
题目地址
讲解
这道题对锻炼递归能力很有帮助。思路如下：如果当前节点大于 R 或小于 L，肯定是要抛弃的。如果大于 R，就返回其左子树（要对左子树继续裁剪），如果小于 L，就返回其右子树（要对右子树继续裁剪）。如果在 L 和 R 之间，就继续遍历其左右进行裁剪。
Java 代码
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) {val = x;}
* }
*/
class Solution {
public TreeNode trimBST(TreeNode root, int L, int R) {
if(root==null){
return root;
}
if(root.val<L){
return trimBST(root.right, L, R);
}else if(root.val>R){
return trimBST(root.left, L, R);
}else{
root.left = trimBST(root.left, L, R);
root.right = trimBST(root.right, L, R);
}
return root;
}
}