javase笔记 基础代码

数组反转

    public static void change(int min,int max,int[] arr) {
	  //使用递归达到数组反转
        if(min >= max){
            return;
        }
        int b;
        b=arr[min];
        arr[min]=arr[max];
        arr[max]=b;
        min++;
        max--;

        change(min,max,arr);
    }

冒泡排序

        //冒泡排序
        //外层循环是比较的次数，内层循环是比较
        for (int a = 0; a < arr.length-1; a++) {
            for (int i2 = 0; i2 < arr.length-a-1; i2++) {
                if(arr[i2]>arr[i2+1]){
                    int tem = arr[i2+1];
                    arr[i2+1]=arr[i2];
                    arr[i2]=tem;
                }
            }
        }

二分查找

package com.atguigu.d_array;

public class Demo04Binary {
    //二分法查找
    //前提要确保数组是有序的
    public static void main(String[] args) {
        int[]arr = {1,2,3,4,5,6,7,8,};
        int result = binary(3,arr);
        System.out.println("result = " + result);


    }

    public static int binary(int a,int[] arr) {
        //定义三个变量
        int min = 0;
        int max = arr.length - 1;
        int mid = 0;
        while(min<=max){
            mid = (min + max) / 2;
            if(a<arr[mid]){
                max=mid-1;
            }else if(a>arr[mid]){
                min = mid+1;
            }else {
                return mid;
            }
        }
        return -1;

    }
}