实现这个函数：
char* strrep(const char* src, const char* from, const char*
to)
{
}
将src中出现的所有from替换成to
时间：
10分钟。
要求：
1.
功能正确，尽量高效
2.不能调用现有的正则表达式库
3.可以使用strdup，malloc，realloc等函数，以及其他的c字符串
操作函数
4.估算你所写算法的时间复杂度
#include <string.h>
#include <malloc.h>
/**
* On success, strrep() returns a newly allocated string, which is constructed by replacing all substring `from' in `src' with `to'.
* If `from' is a null string(with length of 1), then return a duplication of `src'.
*
* On failure
* ENOMEM Insufficient memory is available.
*
* src is a null-terminated string.
* from is a null-terminated string.
* to is a null-terminated string.
*
*/
char* strrep(const char* src, const char* from, const char* to)
{
char *des, *des_cur;
int from_len, to_len, src_len, des_len;
const char *src_cur, *src_end, *occ;
const char **marks;
int mark_len, m, rep_count;
// prepare
from_len = strlen(from);
to_len = strlen(to);
src_len = strlen(src);
if (from_len == 0)
return strdup(src);
// mark all occurence of `from' in `src'
mark_len = 0x4;
marks = (const char**)malloc(sizeof(char*) * mark_len);
if (marks == NULL)
return NULL;
rep_count = 0;
src_cur = src;
while((occ = strstr(src_cur, from)) != NULL) {
rep_count++;
// need more space for mark
if (rep_count > mark_len) {
mark_len << 1;
marks = (const char**)realloc(marks, mark_len);
if (marks == NULL)
return NULL;
}
// mark the position
marks[rep_count - 1] = occ;
// find next occurence from the current position
src_cur = occ + from_len;
}
// construct new string
des_len = src_len + (to_len - from_len) * rep_count;
des = (char*)malloc(des_len + 1);
if (des == NULL)
return NULL;
des_cur = des;
src_cur = src;
m = 0;
if (m < rep_count)
occ = marks[m];
else
occ = NULL;
while(*src_cur) {
if (src_cur != occ)
*des_cur++ = *src_cur++;
else {
// replace `from' with `to'
strncpy(des_cur, to, to_len);
src_cur += from_len;
des_cur += to_len;
// more to replace?
m++;
if (m < rep_count)
occ = marks[m];
else
occ = NULL;
}
}
des_cur = '\0';
free(marks);
return des;
}