0938. Range Sum of Bst

938.二叉搜索树的范围和 #

Difficulty: 简单

给定二叉搜索树的根结点 root，返回值位于范围 [low, high] 之间的所有结点的值的和。

示例 1：

输入：root = [10,5,15,3,7,null,18], low = 7, high = 15
输出：32

示例 2：

输入：root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
输出：23

提示：

树中节点数目在范围 [1, 2 * 104] 内
1 <= Node.val <= 105
1 <= low <= high <= 105
所有 Node.val 互不相同

题解一 #

暴力解法（DFS） #

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int rangeSumBST(TreeNode root, int low, int high) {
        List<Integer> list = new ArrayList<>();
        helper(root, list);
        Integer result = 0;
        for (Integer val : list) {
            if (val < low || val > high) {
                continue;
            }
            result += val;
        }
        return result;
    }

    private void helper(TreeNode node, List<Integer> list) {
        if (node == null) {
            return;
        }
        helper(node.left, list);
        list.add(node.val);
        helper(node.right, list);
    }
}

DFS（深度优先遍历） #

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {

    public int rangeSumBST(TreeNode root, int low, int high) {
        if (root == null) {
            return 0;
        }
        if (root.val < low) {
            return rangeSumBST(root.right, low, high);
        }
        if (root.val > high) {
            return rangeSumBST(root.left, low, high);
        }
        return root.val + rangeSumBST(root.left, low, high) + rangeSumBST(root.right, low, high);
    }
}