LeetCode-Alg-938-Range Sum of BST

LeetCode-Alg-938-Range Sum of BST

Posted by Jae on May 19, 2019

1、题目

Given the root node of a binary search tree, return the sum of values of all nodes with value between L and R (inclusive).

The binary search tree is guaranteed to have unique values.

Example 1:

Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
Output: 32
Example 2:

Input: root = [10,5,15,3,7,13,18,1,null,6], L = 6, R = 10
Output: 23

Note:

The number of nodes in the tree is at most 10000.
The final answer is guaranteed to be less than 2^31.

2、思路

对于一个根节点,可能落在区间内、区间左边和区间右边,所以可以递归计算,满足区间范围的节点和。

3、实现

public class Solution {

public int rangeSumBST(TreeNode root, int L, int R) {
    if (root == null){
        return 0;
    }

    int sum = 0;
    if (root.val >= L && root.val <= R){
        // 递归计算左子树+右子树和
        sum = root.val + rangeSumBST(root.left, L, R) + rangeSumBST(root.right, L, R);
    }else if (root.val < L){
        // 左子树不可能存在满足区间的节点
        sum = rangeSumBST(root.right, L, R);
    }else if (root.val > R){
        // 右子树上不可能存在满足区间的节点
        sum = rangeSumBST(root.left, L, R);
    }
    return sum;
} }