题解 | #农场牛的最佳观赏区间#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param low int整型 
     * @param high int整型 
     * @return int整型
     */
    public int rangeSumBST (TreeNode root, int low, int high) {
        // write code here
        int sum = 0;
        sum = preOrder(root,sum,low,high);
        return sum;
    }

    public int preOrder(TreeNode node,int sum, int low, int high){
        if(node == null){
            return sum;
        }

        if(node.val >= low && node.val <= high ){
            sum += node.val;
        }
        sum = preOrder(node.left,sum,low,high);
        sum = preOrder(node.right,sum,low,high);
        return sum;
    }
}