按值查找之折半查找

折半查找作爲一種高效的查找方法，不應該不掌握它

廢話少說 !上碼

 

#include <iostream>
using namespace std;

int  Binary_find(int *arr,int len,int value)
{
	if(NULL==arr||0==len)
	{
	    return -1;
	}
	int start = 0;
	int end = len-1;
	while(start<=len)
	{
        int mid = start+((end-start)>>1);//左移一位相當於除2
        if(value==arr[mid])
           return arr[mid];
        else if(value > arr[mid])
            start = mid+1;
        else
        	 end=mid-1;
	}  
	return -1;
}

int main()
{
	int a[]={0,1,2,3,4,5,6,7,8,9,10,11,15,45,48};
	int len=sizeof(a)/sizeof(a[0]);
	int b= Binary_find(a,len,45);
	cout<<b<<endl;

}

還有一種遞歸的方法

#include <stdio.h>

int bin_search(int key[],int low, int high,int k)

{

    int mid;

    if(low>high)

        return -1;

    else{

        mid = (low+high) / 2;

        if(key[mid]==k)

            return mid;

        if(k>key[mid])

            return bin_search(key,mid+1,high,k);        /*在序列的後半部分查找*/

        else

            return bin_search(key,low,mid-1,k);            /*在序列的前半部分查找*/

    }

}

 

int main()

{

    int n , i , addr;

    int A[10] = {2,3,5,7,8,10,12,15,19,21};

    printf("The contents of the Array A[10] are\n");

    for(i=0;i<10;i++)

    printf("%d ",A[i]);                                /*顯示數組A中的內容*/

    printf("\nPlease input a interger for search\n");

    scanf("%d",&n);                                /*輸入待查找的元素*/

    addr = bin_search(A,0,9,n);

    if(-1 != addr)                                /*查找成功*/

    printf("%d is at the %dth unit is array A\n ",n,addr);

    else printf("There is no %d in array A\n",n);            /*查找失敗*/

    getchar();

	return 0;

}