class Solution {
public:
//得到前缀表void getNext(int *next,string needle){int j=0;for(int i=1;i<needle.size();i++){while(j>0 && needle[j]!=needle[i]) j=next[j-1];//**j>0**=>j==0是出口if(needle[i]==needle[j]) j++;next[i]==j;//若写入if中，则该行意思变为当匹配时才给next赋值，没能顾及到回退时的赋值}}int strStr(string haystack, string needle) {if(needle.size()==0) return 0;vector<int> next(needle.size());getNext(&next[0],needle);int j=0;for(int i=0;i<haystack.size();i++){while(j>0 && haystack[i]!=needle[j]) j=next[j-1];//运用前缀表if(haystack[i]==needle[j]) j++;if(j==needle.size()) return i-needle.size()+1;}return -1;}
};

find解答

class Solution {
public:int strStr(string haystack, string needle) {return haystack.find(needle);}
};