938. Range Sum of BST

QUESTION:

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.

EXPLANATION:

这个就比较简单le

因为是bst,就是二分查找树,所以当左边小于L时,那这个节点所有的左边都可以放弃了。同理右边。然后进行遍历就行。

如代码:

SOLUTION:

class Solution {
    public int rangeSumBSTResult = 0;
    public int rangeSumBST(TreeNode root, int L, int R) {
        if(root == null) return 0;
        if(root.val<L) {
            rangeSumBST(root.right,L,R);
        }else if(root.val>R){
            rangeSumBST(root.left,L,R);
        }else if(root.val>=L && root.val <=R){
            rangeSumBSTResult+=root.val;
            rangeSumBST(root.right,L,R);
            rangeSumBST(root.left,L,R);
        }
        return rangeSumBSTResult;
    }
}
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