二分法查找

import java.util.Scanner;

public class erfen {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int x = scan.nextInt();
        int[] a= {0,1,2,3,4,5,6,7,8,9,10};
        int i = 0;
        int j= a.length-1;
        int mid=0;
        while(i<=j)
        {
            mid = (i+j)/2;
            if(x==a[mid])
                break;
            if(x>a[mid])
            {
                i=mid+1;
            }
            else{
                j=mid-1;
            }
        }
        System.out.println(a[mid]);
    }
}

分析：i<=j,而不是i<j是因为在i=j时还存在搜索空间i(j)；