leetCode树和链表工具

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网上找的leetCode题目字符串转树和链表的工具，来自原文

一、工具

package com.colin.tool;

import java.util.List;
import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * LeetCode工具
 */
public class LeetCode {

    public static class ListNode {
        public int val;
        public ListNode next;
        public ListNode(int x) {
            val = x;
        }
    }

    public static class TreeNode {
        public int val;
        public TreeNode left;
        public TreeNode right;
        public TreeNode(int x) {
            val = x;
        }
    }

    /**
     * 生成连表
     *
     * @param str
     * @return
     */
    public static ListNode createList(String str){
        if (str==null) return null;
        String substring = str.substring(1, str.length() - 1);
        if (substring.length()==0)return null;
        String[] split = substring.split(",");
        ListNode root = new ListNode(-1);
        ListNode temp = root;
        for (String s : split) {
            ListNode next = new ListNode(Integer.parseInt(s));
            temp.next = next;
            temp = next;
        }
        return root.next;
    }

    /**
     * 生成二叉树
     *
     * @param str
     * @return
     */
    public static TreeNode createTree(String str) {
        if (str==null) return null;
        String substring = str.substring(1, str.length() - 1);
        if (substring.length()==0)return null;
        String[] split = substring.split(",");
        TreeNode root = split[0].equals("null")?null:new TreeNode(Integer.parseInt(split[0]));
        Queue<TreeNode> queue = new LinkedBlockingQueue<>();
        queue.add(root);
        int index = 1;
        while (!queue.isEmpty()){
            TreeNode cur = queue.poll();
            if (index<split.length){
                cur.left = split[index].equals("null")?null:new TreeNode(Integer.parseInt(split[index]));
                index++;
                if (cur.left!=null){
                    queue.add(cur.left);
                }
            }else {break;}
            if (index<split.length){
                cur.right= split[index].equals("null")?null:new TreeNode(Integer.parseInt(split[index]));
                index++;
                if (cur.right!=null){
                    queue.add(cur.right);
                }
            }else {break;}
        }
        return root;
    }
    
    public static void show(List<TreeNode> nodes) {
        nodes.forEach(node-> System.out.print(node.val + ","));
        System.out.println();
    }

    /**
     * 展示二叉树的结构
     *
     * @param root
     */
    public static void show(TreeNode root) {
        if (root == null) System.out.println("EMPTY!");
        // 得到树的深度
        int treeDepth = getTreeDepth(root);

        // 最后一行的宽度为2的（n - 1）次方乘3，再加1
        // 作为整个二维数组的宽度
        int arrayHeight = treeDepth * 2 - 1;
        int arrayWidth = (2 << (treeDepth - 2)) * 3 + 1;
        // 用一个字符串数组来存储每个位置应显示的元素
        String[][] res = new String[arrayHeight][arrayWidth];
        // 对数组进行初始化，默认为一个空格
        for (int i = 0; i < arrayHeight; i ++) {
            for (int j = 0; j < arrayWidth; j ++) {
                res[i][j] = " ";
            }
        }

        // 从根节点开始，递归处理整个树
        // res[0][(arrayWidth + 1)/ 2] = (char)(root.val + '0');
        writeArray(root, 0, arrayWidth/ 2, res, treeDepth);

        // 此时，已经将所有需要显示的元素储存到了二维数组中，将其拼接并打印即可
        for (String[] line: res) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < line.length; i ++) {
                sb.append(line[i]);
                if (line[i].length() > 1 && i <= line.length - 1) {
                    i += line[i].length() > 4 ? 2: line[i].length() - 1;
                }
            }
            System.out.println(sb.toString());
        }
    }

    // 用于获得树的层数
    public static int getTreeDepth(TreeNode root) {
        return root == null ? 0 : (1 + Math.max(getTreeDepth(root.left), getTreeDepth(root.right)));
    }


    private static void writeArray(TreeNode currNode, int rowIndex, int columnIndex, String[][] res, int treeDepth) {
        // 保证输入的树不为空
        if (currNode == null) return;
        // 先将当前节点保存到二维数组中
        res[rowIndex][columnIndex] = String.valueOf(currNode.val);

        // 计算当前位于树的第几层
        int currLevel = ((rowIndex + 1) / 2);
        // 若到了最后一层，则返回
        if (currLevel == treeDepth) return;
        // 计算当前行到下一行，每个元素之间的间隔（下一行的列索引与当前元素的列索引之间的间隔）
        int gap = treeDepth - currLevel - 1;

        // 对左儿子进行判断，若有左儿子，则记录相应的"/"与左儿子的值
        if (currNode.left != null) {
            res[rowIndex + 1][columnIndex - gap] = "/";
            writeArray(currNode.left, rowIndex + 2, columnIndex - gap * 2, res, treeDepth);
        }

        // 对右儿子进行判断，若有右儿子，则记录相应的"\"与右儿子的值
        if (currNode.right != null) {
            res[rowIndex + 1][columnIndex + gap] = "\\";
            writeArray(currNode.right, rowIndex + 2, columnIndex + gap * 2, res, treeDepth);
        }
    }
}

二、使用

// 引入TreeNode和ListNode
import com.colin.tool.LeetCode.*;

// 构造
TreeNode root = LeetCode.createTree("[1,null,2,null,3]");

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