LeetCode-Implement strStr()

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

简单暴力

[code]class Solution {
public:
char *strStr(char *haystack, char *needle) {
if(haystack == NULL || needle == NULL)
return NULL;
int hLen = strlen(haystack);
int nLen = strlen(needle);
if(hLen < nLen)
return NULL;
if(nLen == 0) //"", ""   return ""
return haystack;
for(int i=0;i < hLen-nLen+1; i++){//只要循环hLen-nLen+1次，因为这之后主串的位数少于nLen，也就不可能找到子串了
int index = i;
int j = 0;
while(j < nLen && haystack[index] == needle[j]){
j++;
index++;
}
if(j == nLen)
return haystack+i;
}
return NULL;
}
};

如果不允许用strlen等库函数，可采用以下代码

char* StrStr(const char *str, const char *target) {
if (!*target) return str;
char *p1 = (char*)str, *p2 = (char*)target;
char *p1Adv = (char*)str;
while (*++p2)
p1Adv++;
while (*p1Adv) {
char *p1Begin = p1;
p2 = (char*)target;
while (*p1 && *p2 && *p1 == *p2) {
p1++;
p2++;
}
if (!*p2)
return p1Begin;
p1 = p1Begin + 1;
p1Adv++;
}
return NULL;
}