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有一个字符数组的内容为:"student a am i",
请你将数组的内容改为"i am a student".
要求：
不能使用库函数。
只能开辟有限个空间（空间个数和字符串的长度无关）。

student a am i
i ma a tneduts
i am a student
 

#include <stdio.h>
#include <string.h>
#include <assert.h>
char * fanzhuan(char *str)
{
    assert(str);
    char *l = str;
    char *r = str;
    while(*r != '\0')
    {
        r++;
    }
    while(l < r-1)
    {
        char tmp = *l;
        *l = *(r-1);
        *(r-1) = tmp;
        l++;
        r--;
    }
    l = str;
    r = str;
    while(*r != '\0')
    {
        while(*r != 32 && *r != '\0')
        {   
            r++;
        }
        char *p = r;
        while(l < r-1)
        {
            char tmp = *l;
            *l = *(r-1);
            *(r-1) = tmp;
            l++;
            r--;
        }
        if(*p == '\0')
        {
            return str;
        }
        l = p+1;
        r = p+1;
    }
    return str;
}

int main ()
{
    char a[] = "student a am i";
    char *ret = fanzhuan(a);
    printf("%s\n",ret);
    return 0;
}