面试题30：KMP 字符串查找

参考：http://www.ruanyifeng.com/blog/2013/05/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm.html
自己写的很简单的KMP字符串匹配

 int KMP(string s,string p){
     int pLen = p.length();
     int* next = new int[pLen];
     next[] = -;

     int k = -;
     int j = ;
     while(j < pLen - ){
         if(k == - || p[k] == p[j]){
             k++;
             j++;
             next[j] = k;
         }else{
             k = next[k];
         }
     }

     //print next array;
     for(int k=;k<pLen;k++){
         std::cout << next[k]<< ",";
     }
     std::cout << std::endl;

     j = ;
     size_t i = ;
     size_t sLen = s.length();
     while(i<sLen && j < pLen){
         if(j == - || s[i] == p[j]){
             i++;
             j++;
         }else{
             j = next[j];
         }
     }

     delete next;
     if(j == pLen){
         return i - j;
     }else{
         return -;
     }
 }

Implement strStr().

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

 class Solution {
 public:
     char *strStr(char *haystack, char *needle) {
         if(haystack == nullptr || needle == nullptr) return nullptr;

         int i = ,j =;
         int start = ;
         while(haystack[i] != '\0' && needle[j] != '\0'){
             if(haystack[i] == needle[j]){
                 i++;
                 j++;
             }else{
                 start++;
                 i = start;
                 j = ;
             }
         }
         if(needle[j] == '\0') return haystack+start;
         else return nullptr;
     }
 };