c语言 9-5

1、线性查找法

#include <stdio.h>

#define FAILED -1

int len(char x[])
{
    int len = 0;
    while(x[len])
        len++;
    return len;
}

int search(char x[], char key)
{
    int i = 0;
    while(1)
    {
        if(i == len(x))
            return FAILED;
        if(x[i] == key)
            return i;
        i++;
    }
}

int main(void)
{
    char str[128];
    printf("str: "); scanf("%s", str);
    printf("position: %d
", search(str, 'c'));
    return 0;
}

2、线性查找法

#include <stdio.h>

#define FAILED -1

int len(char x[])
{
    int i = 0;
    while(1)
    {
        if(x[i] == '')
            return i;
        i++;
    }
}

int search(char x[], char key)
{
    int i = 0;
    while(1)
    {
        if(i == len(x))
            return FAILED;
        if(x[i] == key)
            return i;
        i++;
    }
}

int main(void)
{
    char str[128];
    printf("str: "); scanf("%s", str);
    printf("position: %d
", search(str, 'c'));
    return 0;
}

3、线性查找法

#include <stdio.h>

#define FAILED -1

int length(char x[])
{
    int i = 0;
    while(1)
    {
        if(x[i] == '')
            return i;
        i++;
    }
}

int search(char x[], char key)
{
    int len, i;
    len = length(x);
    for(i = 0; i < len; i++)
    {
        if(x[i] == key)
            return i;
    }
    if(i == len)
        return FAILED;
}

int main(void)
{
    char str[128];
    printf("str: "); scanf("%s", str);
    
    printf("position: %d
", search(str, 'c'));
    return 0;
}

4、哨兵查找法

#include <stdio.h>

#define FAILED -1

int length(char x[])
{
    int i = 0;
    while(1)
    {
        if(x[i] == '')
            return i;
        i++;
    }
}

int search(char x[], char key)
{
    int len = length(x);
    x[len] = key;
    int i = 0;
    while(1)
    {
        if(x[i] == key)
            break;
        i++;
    }
    return i < len ? i : FAILED;
}

int main(void)
{
    char str[128];
    printf("str: "); scanf("%s", str);
    printf("pos: %d
", search(str, 'c'));
    return 0;
}

5、简化

#include <stdio.h>

#define FAILED -1

int search(char x[], char key)
{
    int i = 0;
    while(1)
    {
        if(x[i] == key)
            return i;
        if(x[i] == '')
            return FAILED;
        i++;
    }
}

int main(void)
{
    char str[128];
    printf("str:  "); scanf("%s", str);
    printf("pos:  %d
", search(str, 'c'));
    return 0;
}