[Java-알고리즘] RangeSumBinaraySearchTree

[Problem]

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.

 

[Example1]

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

 

[Example2]

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

 

[Note]

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

 

[Solution]

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int rangeSumBST(TreeNode root, int L, int R) {
        if(root == null){
            return 0;
        }
        
        if(root.val < L){
            return rangeSumBST(root.right, L, R);
        }
        
        if(root.val > R){
            return rangeSumBST(root.left, L, R);
        }
        
        return root.val + rangeSumBST(root.right, L, R) + rangeSumBST(root.left, L, R);
    }
}

 

 

 

 

오랜만에 트리 문제를 풀었다. DFS로 풀면 된다.  자료구조 개념들을 좀 잊은 것 같아서 다시 봐야겠다는 생각이 들었다.