字符串HASH

字符串哈希方法很多。

当字符串很多，但是不同得却很小时候，利用字符串HASH很方便。而不用大费内存去用MAP。有时侯

还可能使MLE。

详细字符串HASH讲解。

http://www.cnblogs.com/atlantis13579/archive/2010/02/06/1664792.html

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<time.h>

#define HASH 1000003
int head[HASH];
char str[1000][40];

int hash( char *str)
{
  int h = 0, seed = 131;
  while( *str )
  {
     h = h * seed + *(str++);
  }
  return ( h & 0x7fffffff) % HASH;
}

int main( )
{
  int N;
  char sample[100] = "hello,world! welcome you --";
  int len = strlen(sample);
  srand(time(NULL));
  while( scanf("%d",&N) != EOF )
  {
     int n = 1;
     memset(head, -1,sizeof(head));
     for( int i = 0; i < N; i++)
     {
        char ch = rand() % 26 + 'A'; 
        char st = rand() % 26 + 'A';
        sample[len] = ch;
        sample[len+1] =st;
        sample[len+2] = '\0';
        printf("input:%s\n", sample);
        int x = hash( sample );
        if( head[x] != -1 )
        printf("成功找到已存字符串:%s\n", str[head[x]]);
        else
        {
           head[x] = n;
           strcpy(str[n], sample);
           n++;
        }     
     }

  }
  return 0;
}