KMP算法

#include <iostream>
#include <cstring>
#include <string>
using namespace std;

int* getnext(int n,string c)
{
 int* next = new int[n];
 next[0] = -1;
 int i = 0;
 int k = -1;
 while (i < n - 1)
 {
  // int k = next[i];这是错误的。优化next数组的k应该用满足条件的最大的k值，不能更新为next[i]
  while (k >= 0 && c[i] != c[k])
   k = next[k];
  i++;
  k++;     //保存较大的k值，在下次循环中使用
  next[i] = k;
  if (c[i] == c[k])
   next[i] = next[k];
 }
 return next;
}

int main()
{
 string t;
 string p;
 cin >> t >> p;
 int np = p.size();
 int nt = t.size();
 int* next = getnext(np, p);
 int i = 0;
 int j = 0;
 while (i < nt&&j < np)
 {
  if (t[i] == p[j] || j == -1)    //如果j等于-1，则说明第一个都无法匹配，则直接用第0个元素和t串中第i+1个元素进行对比
  {
   i++;
   j++;
  }
  else
  {
   j = next[j];
  }
 }
 if (j == np)
  cout << "Oh~~~~~~" << endl;
 else
  cout << "NO" << endl;
 return 0;
}