938. Range Sum of BST

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.

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:

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.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void rangeSumBSTHelper(TreeNode* root, int L, int R,int& sums){
        if(root!=nullptr){
            if(root->val>=L&&root->val<=R){
                sums+=root->val;
                rangeSumBSTHelper(root->left,L,R,sums);
                rangeSumBSTHelper(root->right,L,R,sums);
            }else if(root->val<L){
                rangeSumBSTHelper(root->right,L,R,sums);
            }else{
                rangeSumBSTHelper(root->left,L,R,sums);
            }
        }
    }
    int rangeSumBST(TreeNode* root, int L, int R) {
        int result=0;
        rangeSumBSTHelper(root,L,R,result);
        return result;
    }
};

static auto speedup = [](){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    return nullptr;
}();

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