NO6——KMP

 int next[N];
 char str1[M],str2[N];
 //str1 长，str2 短
 //len1,len2,对应str1,str2的长

 void get_next(int len2)
 {
     int i = ,j = -;
     next[] = -;
     while(i<len2)
     {
         if(j == - || str2[i] == str2[j])
         {
             i++;
             j++;
             if(str2[i] != str2[j])
                 next[i] = j;
             else
                 next[i] = next[j];
         }
         else
             j = next[j];
     }
     //计算某字符串的周期，如aaaa是4，abcd是1
     /*
     int i = 0;j = -1;
     next[0] = -1;
     while(str2[i])
     {
         if(j == -1 || str2[i] == str2[j])
         {
             i++;j++;
             next[i] = j;
         }
         else
         j = next[j];
     }
     len = strlen(str);
     i = len-j;
     if(len%i==0)
     return len/i;
     else
     return 1;
     */
 }

 int kmp(int len1,int len2)
 {
     int i = ,j = ;
     get_next(len2);
     while(i<len1)
     {
         if(j == - || str1[i] == str2[j])
         {
             i++;
             j++
         }
         else
             j = next[j];
         /*
                 if(j == len2)//计算str2在str1中出现多少次
                 {
         cnt++;
         j= next[j];
                 }
                 */
     }
     //return j; //j为匹配的长度
     if(j>len2)
         return ;//这里也可以返回i-len2来获得匹配在主串中开始的位置
     else
         return ;
 }

 //数字KMP
 int a[],b[];
 int next[],n,m;

 void getnext()
 {
     int i = ,j = -;
     next[] = -;
     while(i<m)
     {
         if(j == - || b[i] == b[j])
         {
             i++;
             j++;
             if(b[i] == b[j])
             next[i] = next[j];
             else
             next[i] = j;
         }
         else
         j = next[j];
     }
 }

 int kmp()//返回匹配位置
 {
     int i = ,j = ;
     while(i<n)
     {
         if(a[i] == b[j])
         {
             if(j == m-)
             return i-j+;
             i++;
             j++;
         }
         else
         {
             j = next[j];
             if(j == -)
             {
                 i++;
                 j = ;
             }
         }
     }
     return -;
 }