KMP算法的重点是寻找next数组，程序如下：

#include <iostream>  #include <string>  #include <vector>  using namespace std;    class Solution  {  public:      int KMPSearch(string text, string pattern, vector<int> next)      {          int i = 0;          int j = 0;          while (i<text.size() && j<int(pattern.size()))          {              if (j == -1 || pattern[j] == text[i])              {                  i++;                  j++;              }              else              {                  j = next[j];              }          }            if ( j == pattern.size())              return i - j;          else              return -1;      }        void GetNext(string pattern, vector<int>& next)      {           next[0] = -1;          int start = -1;          int end = 0;          while (end < pattern.size() - 1)          {              if (start == -1 || pattern[start] == pattern[end])              {                  ++start;                  ++end;                  next[end] = start;              }              else              {                  start = next[start];              }          }      }  };    int main()  {      Solution sol;      vector<int> next(7, 0);      string text("AAAAABBC ABCDAB ABCDABBDCDABDE ABCDABD");      string pattern("ABCDABD");      sol.GetNext(pattern, next);      cout << sol.KMPSearch(text, pattern, next) << endl;  }