poj 3461 - Oulipo 经典kmp算法问题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>

using namespace std;
int ans;
const int maxn = 1000005;
int next[maxn];
char S[maxn],P[maxn];


//构造next数组
void get_next()
{
      int i = 0 ;
      int j = -1;
      
      int lenp = strlen(P); //要用额外变量，如果写在while循环中就会TLE
      
      next[0] = -1;
      
      while(i < lenp)
      {
            if(j == -1 || P[i] == P[j])
            {
                  i++;
                  j++;
                  next[i] = j;
            }
            else
                  j = next[j];
      }
}

//开始模式匹配
void kmp()
{
      int i = 0 ;
      int j = 0 ;
      
      //要用额外变量，如果写在while循环中就会TLE
      int lens = strlen(S);
      int lenp = strlen(P);
      
      get_next();  //这个构造不能忘记写
      
      while(i < lens && j < lenp)
      {
            if(j == -1 || P[j] == S[i])
            {
                  i++;
                  j++;
            }
            else
                  j = next[j];
            if(j == lenp)
            {
                  ans++;
                  j = next[j];
            }
      }
}
int main()
{
    int cas;
    cin >> cas;
    
    while(cas--)
    {
          ans = 0;
          memset(next,0,sizeof(next));
          scanf("%s%s",P,S);
          kmp();
          cout << ans << endl;
    }
    return 0;
}