Poj 1200 Crazy Search (string hash)

Question:

Analyzes the number of substrings with a length of N.

Train of Thought Analysis:

Assign a number to a character that does not appear.

Then, the substring is treated as the number in the NC hexadecimal format.

Then judge by hash.

#include <cstdio>#include <iostream>#include <algorithm>#include <map>#include <cstring>#include <string>using namespace std;bool vis[26666666];int val[30];char str[1111111];int main(){    int n,nc;    while(scanf("%d%d",&n,&nc)!=EOF)    {        scanf("%s",str);        memset(vis,0,sizeof vis);        memset(val,0,sizeof val);        int len=strlen(str);        int cnt=1;        int ans=0;        for(int i=0;i+n<=len;i++)        {            int sum=0;            for(int j=i;j<i+n;j++)            {                if(!val[str[j]-'a'])val[str[j]-'a']=cnt++;                sum*=nc;                sum+=val[str[j]-'a'];            }            if(!vis[sum])            {                ans++;                vis[sum]=true;            }        }        printf("%d\n",ans);    }    return 0;}