Java--算法--实战题目

题目一：

package com.model.tree;

/**
 * @Description:测试类
 * @Author: 张紫韩
 * @Crete 2021/8/15 16:14
 * 根据树的后序遍历，的到原来的树
 */
public class TreeDemo01 {
    public static void main(String[] args) {
        int[] arr={2,4,3,6,8,7,5};
        TreeNode treeNode = buildTree(arr, 0, arr.length - 1);
        System.out.println(treeNode);

    }

    public  static TreeNode buildTree(int[] arr,int left,int right){
        if (left>right) return null;

        if (left==right){
            return new TreeNode(arr[right]);
        }else {
            TreeNode resTree=new TreeNode(arr[right]);
//可以使用二分法得到第一个大于 arr[right]的下标mid
            int mid = right-1;
            for (int i = left; i < right; i++) {
                if (arr[i]>arr[right]){
                    mid=i;
                    break;
                }
            }
            TreeNode leftNode = buildTree(arr, left, mid-1);
            TreeNode rightNode = buildTree(arr, mid, right-1);
            resTree.setLeft(leftNode);
            resTree.setRight(rightNode);
            return resTree;
        }

    }
}
//树节点
class TreeNode{
    private int val;
    private TreeNode left;
    private TreeNode right;

    public TreeNode() {
    }

    public TreeNode(int val) {
        this.val = val;
    }

    public TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }

    public int getVal() {
        return val;
    }

    public void setVal(int val) {
        this.val = val;
    }

    public TreeNode getLeft() {
        return left;
    }

    public void setLeft(TreeNode left) {
        this.left = left;
    }

    public TreeNode getRight() {
        return right;
    }

    public void setRight(TreeNode right) {
        this.right = right;
    }

    @Override
    public String toString() {
        return "TreeNode{" +
                "val=" + val +
                ", left=" + left +
                ", right=" + right +
                '}';
    }
}

题目二：

package com.model.question;

/**
 * @Description:测试类
 * @Author: 张紫韩
 * @Crete 2021/8/16 10:59
 * 两个字符串是否是同源异构的
 * 同源异构：即两个字符串有相同的字母并且字母数量也相等组成
 *
 * 一个字符串的子串是否是另一个字符串的同源字符串 abcbca : abc
 */
public class QuestionDemo03 {
    public static void main(String[] args) {
        System.out.println(isSame("abcabac", "aabbcca"));

        System.out.println(isInclude("abcdeefgjkl", "abc"));

    }
//    使用是窗口的方式解决问题，检测str1字串的子串是否是另一个字符串str2的同源字符串
    public static boolean isInclude(String str1,String str2){
        if (str1.length()<str2.length()){
            return false;
        }
        int[] count=new int[256];
        int len1 = str1.length();
        int len2 = str2.length();
        char[] char1 = str1.toCharArray();
        char[] char2 = str2.toCharArray();
        int flag=0;
//        形成欠债表
        for (char c2:char2){
            count[c2]++;
        }

//        第一个窗口是否是进行还债
        for (int i = 0; i < len2; i++) {
            if (count[char1[i]]--<=0){
                flag++;
            }
        }
//        判断第一个窗口是否是和str2同源
        if (flag==0) {System.out.println("index:"+0); return true;}

//       窗口向后移动，判断后面的窗口是否是同源的
        for (int i = len2; i <len1; i++) {
//            将原来窗口的第一个取出
            if (count[char1[i-len2]]++<0){
              flag--;
            }
//            将窗口的后面一个加入
            if (count[char1[i]]--<=0){
                flag++;
            }
//            判断当前窗口的字符串是否是同源
            if (flag==0){
                System.out.println("index:"+(i-len2+1));
                return true;
            }
        }
        return false;
    }





//    简单的判断两个字符串是否是同源字符串
    public static boolean isSame(String str1,String str2){
        if (str1.length()!=str2.length()) return false;
        int[] temp=new int[256];
        char[] char1 = str1.toCharArray();
        char[] char2 = str2.toCharArray();
        for (char c1:char1){
            temp[c1]++;
        }
        for (char c2:char2){
            if (temp[c2]==0){
                return false;
            }
            temp[c2]--;
        }
        return true;
    }
}

题目三：

题目四：

package com.model.tree;

import com.sun.jmx.remote.internal.ArrayQueue;
import sun.misc.Queue;

import java.awt.*;
import java.util.ArrayDeque;
import java.util.ArrayList;

/**
 * @Description:测试类
 * @Author: 张紫韩
 * @Crete 2021/8/25 23:02
 * 二叉树的层序遍历
 */
public class TreeDemo03 {
    public static void main(String[] args) {

        TreeNode head = new TreeNode(0);
        head.left=new TreeNode(1);
        head.right=new TreeNode(2);
        head.right.right=new TreeNode(3);
        head.right.right.right=new TreeNode(4);

        traverse(head);

    }

//    使用队列实现对树 的层序遍历
    public static void traverse(TreeNode head){
        if (head==null){
            return;
        }
        ArrayList<ArrayList<TreeNode>> resList = new ArrayList<>();

        ArrayDeque<TreeNode> deque = new ArrayDeque<>();
        deque.addLast(head);
        int size;
        while (!deque.isEmpty()){
            size=deque.size();
            ArrayList<TreeNode> temp = new ArrayList<>();
            for (int i = 0; i <size ; i++) {
                TreeNode node = deque.pollFirst();
                temp.add(node);
                if (node.left!=null) deque.addLast(node.left);
                if (node.right!=null) deque.addLast(node.right);
            }
            resList.add(temp);
        }

        System.out.println(resList);
    }
}

posted @ 2021-08-25 23:20 张紫韩阅读(67) 评论(0) 编辑收藏举报

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Java--算法--实战题目

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