day09 数组复制 扩容 二维数组 方法格式

升序排序 Arrays.sort(); 

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数组二分查找

package day09.array;

import java.util.Scanner;

/**
 * 二分查找
 *   long start = System.currentTimeMillis()
 */
public class ArrayDemo06 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int arr[] = {1,5,9,45,88,102,555};
        int max = arr.length-1;
        int min = 0;
        int mid = (max+min)/2;
        int num = scan.nextInt();
        while (num !=arr[mid]){


            if (num > arr[mid]){
                min = mid+1;
                mid = (max+min)/2;
            }else if(num < arr[mid]){
                max = mid -1;
                mid = (max+min)/2;
            }

//            if (min > max){
//                break;
//            }


        }
        if (min <= max){
            System.out.println("找到了"+mid);
        }else {
            System.out.println(-1);
        }

    }
}

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数组的复制 System.arraycopy

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数组的扩容   arr = Arrays.copyOf(arr,10);

会改变数组地址

 

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二维数组

增强for循环遍历数组

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二维数组  格式

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方法