折半查找c代碼

① 用c語言實現折半查找

#include<stdio.h>

int find(int a[],int x,int n,int m)

{int i;

if(n>m)return -1;

i=(n+m)/2;

if(a[i]==x)return i;

if(a[i]>x)return find(a,x,n,i-1);

return find(a,x,i+1,m);

}

int main()

{

襲

int a[20]={2,3,6,7,12,18,19,21,25,28,30,33,37,39,42,45,47,49,50,51};

int x,i;

printf("已有的數是： ");

for(i=0;i<20;i++)

printf("%d ",a[i]);

printf(" 請輸入要查找的數：");

scanf("%d",&x);

if((i=find(a,x,0,19))>=0)

printf("%d是第%d個數 ",x,i+1);

else printf("未找到%d ",x);

return 0;

}

② c語言編程實現「折半查找」的過程。

//參考代碼如下：
#include <stdio.h>
int main()
{
int i, j, n, k=0, isFound=0;
int num[15] = {88,86,75,74,61,56,52,43,39,34,31,22,18,16,8}; //測試數組
printf("請輸出一個整數：\n");
scanf("%d", &n);
i = (int)15/2; //對折位移量
j = (int)15/2; //取數「指針」
while(k<2)
{
i = (int)i/2;
if(i == 0) k++; //i==0 即折半到無可再折時，仍有最後一次比較，故以k做計數
//若未相等，計算下一循環指針的位置
if(n<num[j])
j = j + (i + 1);
else if(n>num[j])
j = j - (i + 1);
else
{
isFound = 1;
break; //若找到相等數，標記已找到並退出循環
}
}
//輸出結果
if(isFound)
printf("該數是數組中第%d個元素的值\n", j);
else
printf("查無此數！\n");
return 0;
}

③ C語言實現折半查找

#include<stdio.h>
intlook_up(inta[],intn,intx)
{
intleft=0,right=n-1,mid;
while(left<=right)
{
mid=(left+right)/2;
if(x==a[mid])
returnmid+1;//加一後才回是它的邏輯答位序
elseif(x<a[mid])
right=mid-1;
else
left=mid+1;
}
if(left>right)
return-1;
}
intmain()
{
inta[100],n,x,i,result;
scanf("%d",&n);
for(i=0;i<n-1;i++)
scanf("%d,",&a[i]);
scanf("%d",&a[i]);
scanf("%d",&x);
result=look_up(a,n,x);
if(result>=0)
printf("%d ",result);
else
printf("No ");
}