## 各种基本算法实现小结（六）—— 查找算法

（均已测试通过）

===================================================================

1、简单查找

```#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAX 101
void input(int num[])
{
int i;

srand((unsigned)time(NULL));
for(i=1; i<MAX; i++)
num[i]=rand()%100;
}
void output(int num[])
{
int i;

for(i=1; i<MAX; i++)
{
printf("%5d", num[i]);
if(0==i%10)
printf("/n");
}
}
int find(int num[], int x)
{
int i;
for(i=1; i<MAX; i++)
if(x == num[i])
return i;
return 0;
}
void main()
{
int x, pos, num[MAX];
input(num);

printf("num...: /n");
output(num);

printf("Enter find num: ");
scanf("%d", &x);
pos=find(num, x);
if(pos)
printf("OK! %d is found in pos: %d/n", x, pos);
else
}
```

==========================================================

2、 折半查找

```#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAX 101
void input(int num[])
{
int i;

srand((unsigned)time(NULL));
for(i=1; i<MAX; i++)
num[i]=rand()%100;
}
void output(int num[])
{
int i;

for(i=1; i<MAX; i++)
{
printf("%5d", num[i]);
if(0==i%10)
printf("/n");
}
}
void sort(int num[], int low, int high) /* quick sort */
{
int l, h;

if(low<high)
{
l=low;
h=high;
num[0]=num[l]; /* save pivot */

while(l<h)
{
while(l<h && num[h]>=num[0]) h--;
num[l]=num[h];
while(l<h && num[l]<=num[0]) l++;
num[h]=num[l];
}
num[l]=num[0]; /* insert pivot */

sort(num, low, l-1);
sort(num, l+1, high);
}
}
int find(int num[], int x, int low, int high)
{
int mid;

while(low<=high)
{
mid=(low+high)/2; /* find is OK */

if(x==num[mid])
return mid;
else if(x<num[mid])
high=mid-1;
else
low=mid+1;
}
return 0;
}
void main()
{
int x, pos, num[MAX];
input(num);

printf("sort before... /n");
output(num);
sort(num, 1, MAX-1);
printf("sort after... /n");
output(num);

printf("Enter find num: ");
scanf("%d", &x);
pos=find(num, x, 1, MAX-1);
if(pos)
printf("OK! %d is found in pos: %d/n", x, pos);
else
}
```

==========================================================