用这题复习下kmp算法。kmp网上坑爹的是有很多种匹配方式，容易混淆，后人要警惕啊。这里对要查找的字符串的next全部置为-1，预处理时i和next[i-1]+1相比较。和http://kb.cnblogs.com/page/176818/ 这里相似。预处理完再匹配，第i个字符不匹配则比较第next[i-1]+1个。
class Solution{
public:
char *strStr(char *haystack, char *needle){
if(haystack == NULL || needle == NULL)
return NULL;
int sz = strlen(needle);
vector<int>next(sz,-1);
for(int i = 1; i < sz; i++){
int index = i - 1;
while(index != -1 && needle[next[index]+1] != needle[i])
index = next[index];
next[i] = index==-1?-1:next[index]+1;
}
int i = 0;
while(*haystack && i <sz){
while(i != -1 && *haystack != needle[i])
i = i==0?-1:next[i-1]+1;
haystack++;
i++;
}
return i < sz?NULL:haystack-sz;
}
};
/* a b C b C a d
-1 -1 -1 -1 -1 0 -1
abcab cabdabba
a b c a b d
-1 -1 -1 0 1 -1*/