/*
3.使用二分法查找有序數組中元素。找到返回索引，不存在輸出-1。使用遞歸實現
*/
import java.util.Scanner;
public class Recursion{
public static void main(String[]args)
{
System.out.println("請輸入要找的整數");
Scanner sc=new Scanner(System.in);
int num = sc.nextInt();
int []a={1,2,3,4,5,6,7,8,9};
int front = 0;
int end = a.length-1;
int mid = (front+end)/2;
//遞歸實現二分法
int index=findArray(a,front,mid,end,num);
if(index!=-1)
{
System.out.println("找到該數"+index);
}
else
{
System.out.println(index);
}
}
public static int findArray(int[]b,int front,int mid,int end,int num)
{
int index = -1;
if(front==end)
{
if(b[mid]==num)
{
return mid;
}
else
{
return index;
}
}
else if(front<end)
{
if(b[mid]==num)
{
index = mid;
return index;
}
else if(b[mid]>num)
{
end = mid-1;
mid = (front+end)/2;
return findArray(b,front,mid,end,num);
}
else if(b[mid]<num)
{
front=mid+1;
mid=(front+end)/2;
return findArray(b,front,mid,end,num);
}
}
//爲什麼下面的else需要註釋掉，不註釋掉編譯會報錯說缺少返回值
else
{
return index;
}
// return index;
}
}爲什麼程序的報錯，說else語句之後缺少返回值