938. Range Sum of BST

QUESTION:

Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [low, high].

Example 1:

``````Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32
Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32.
``````

Example 2:

``````Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23
Explanation: Nodes 6, 7, and 10 are in the range [6, 10]. 6 + 7 + 10 = 23.
``````

Constraints:

``````The number of nodes in the tree is in the range [1, 2 * 104].
1 <= Node.val <= 105
1 <= low <= high <= 105
All Node.val are unique.
``````

EXPLANATION:

1. 将所有值都取出来放在一个数组中
2. 对数组中的值进行范围判断
3. 如果在范围中就进行累加操作

SOLUTION:

``````class Solution {
func rangeSumBST(_ root: TreeNode?, _ low: Int, _ high: Int) -> Int {
var result:Int = 0;
var vals:[Int] = []
rangeSumBSTHelper(root, result: &vals)
vals.forEach{ val in
if (val >= low && val <= high) {
result += val
}
}
return result
}

func rangeSumBSTHelper(_ root: TreeNode?, result: inout [Int]) {
if (root == nil) {
return
}
result.append(root!.val)
rangeSumBSTHelper(root?.left, result: &result)
rangeSumBSTHelper(root?.right, result: &result)
}
}
``````
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