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:

也没有什么特别可说的.

  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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