折半查找法

import java.math.BigInteger;
import java.util.Arrays;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        int[] a = {0,5,7,9,12,16,19,20,22,23};
        f(a,1,9,19);
    }
    public static void f(int[] a,int l,int r,int b){
        int mid = (l+r)/2;
        if(a[mid]==b){
            System.out.println(mid);
            return;
        }else if(a[mid]>b){
            f(a,l,mid,b);
        }else{
            f(a,mid,r,b);
        }
    }
}