加载二进制树替换一个Leetcode为您提供

Question

我已经在Leetcode上完成了以下问题：https://leetcode.com/problems/binary-tree-preorder-traversal/description/，但希望能够在我的IDE中编写类似的问题，这样我就可以立即看到语法错误。问题是Leetcode为您提供了二叉树，您只需编写类Solution，因此我不确定如何创建二进制树并将其加载到Solution。

package cs_gator_problem_classification;

import java.util.ArrayList;
import java.util.Stack;

import com.sun.xml.internal.bind.v2.schemagen.xmlschema.List;

public class PreorderTraversal_Problem1 {       

     //Definition for a binary tree node.
     static class TreeNode {
         int val;
         TreeNode left;
         TreeNode right;
         TreeNode(int x) { val = x; }
     }

    static class Solution {
        public ArrayList<Integer> preorderTraversal(TreeNode root) {
            Stack<TreeNode> s = new Stack<TreeNode>();
            ArrayList<Integer> result = new ArrayList<Integer>();

            s.push(root);

            while(!s.empty()) {
                TreeNode current = s.peek(); 
                s.pop();

                if(current != null) {
                    s.push(current.right);
                    s.push(current.left);

                    result.add(current.val);
                }
            }

            //result.add(1);
            System.out.println("result: " + result);
            return result;
        }
    }

    public static void main(String[] args) {
        System.out.println("test");
        TreeNode originalRoot = new TreeNode(3); 
        Solution solution = new Solution();
    }
}

Answer 1

so I'm not sure how to create and load the binary tree into Solution

1。创建二叉树

以下是两种简单的方法，您可以为给定的根对象创建二叉树。您可以通过设置新的左\右节点来制作您喜欢的任何类型的数据。

public static void makeTreeData(TreeNode root) {
    if (null == root) {
        throw new IllegalArgumentException("root should not be null.");
    }
    if (root.val > 10) {
        return;
    }
    TreeNode left = new TreeNode(root.val * 2);
    makeTreeData(left);
    TreeNode right = new TreeNode(root.val * 2 + 1);
    makeTreeData(right);

    root.left = left;
    root.right = right;
}

public static void makeTreeData2(TreeNode root) {
    root.right = new TreeNode(2);
    root.right.left = new TreeNode(3);
}

2。将二叉树加载到Solution

中

只需使用刚创建的TreeNode调用solution.preorderTraversal(TreeNode)方法即可。你可以在控制台中看到结果。

public static void main(String[] args) {
    System.out.println("test");
    TreeNode originalRoot = new TreeNode(3); 
    Solution solution = new Solution();
    System.Out.println(solution.preorderTraversal(originalRoot));
}