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.

实现KMP

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(haystack==NULL||needle==NULL)return NULL;
        if(needle[0]=='')return haystack;
        int len=0;
        for(;;){if(needle[len]=='')break;len++;}
        vector<int> dict;
        dict.resize(len);
        dict[0]=-1;
        dict[1]=0;
        for(int i=2;i<len;i++){
            int j=dict[i-1];
            while(j>=0&&needle[j]!=needle[i-1]){
                j=dict[j];
            }
            if(j<0)j=0;
            else if(needle[j]==needle[i-1]){
                j++;
            }
            dict[i]=j;
        }
        int i=0,j=0;
        while(haystack[i]!='')
        {
            while(j>=0&&haystack[i]!=needle[j]){
                j=dict[j];
            }
            j++;
            if(j==len){
                return &haystack[i-len+1];
            }
            i++;
        }
        return NULL;
    }
};