插值查找和折半（二分）查找

插值查找

#include <stdio.h>

int bin_search( int str[], int n, int key )
{
    int low, high, mid;
    
    low = 0;
    high = n-1;

    while( low <= high )
    {
        mid = low + (key-a[low]/a[high]-a[low])*(high-low); // 插值查找的唯一不同點
        
        if( str[mid] == key )
        {
            return mid;              
        }
        if( str[mid] < key )
        {
            low = mid + 1;       
        }
        if( str[mid] > key )
        {
            high = mid - 1;       
        }
    }

    return -1;                      
}

int main()
{
    int str[11] = {1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89};
    int n, addr;

    printf("請輸入待查找的關鍵字: ");
    scanf("%d", &n);

    addr = bin_search(str, 11, n);
    if( -1 != addr )
    {
        printf("查找成功，可喜可賀，可口可樂! 關鍵字 %d 所在的位置是: %d\n", n, addr);
    }
    else
    {
        printf("查找失敗!\n");
    }

    return 0;
}

折半（二分）查找：

#include<stdio.h>
int BinSearch(int arr[],int len,int key)                          //折半查找法（二分法）
{
	int low=0;                         //定義初始最小
	int high=len-1;                 //定義初始最大
	int mid;                            //定義中間值
	while(low<=high)
	{
		mid=(low+high)/2;              //找中間值
		if(key==arr[mid])               //判斷min與key是否相等
			return mid;    
		else if(key>arr[mid])             //如果key>mid  則新區間爲[mid+1,high]
			low=mid+1;
		else                                       //如果key<mid  則新區間爲[low,mid-1]
			high=mid-1;
	}
	return -1;                             //如果數組中無目標值key，則返回 -1 ；
}
int main()
{
	int arr[]={1,2,3,4,5,6,7,8,9,10,11};                      //首先要對數組arr進行排序
	printf("%d \n",BinSearch(arr,(sizeof(arr)/sizeof(arr[0])),7));
	return 0;
}