hash

Posted 2021-03-01 reshuffle

char s[maxn];
int len;
const ull base=233;
ull hashsum[maxn];
ull pw[maxn];
void hash_init()
{
    pw[0]=1;
    hashsum[0]=1;//
    for (int i=1;i<=len;i++) pw[i]=pw[i-1]*base;//hash power
    for (int i=1;i<=len;i++) hashsum[i]=hashsum[i-1]*base+s[i-1];//hash: hashsum[i] <- s[i-1]
}
ull gethash(int i,int j)
{
    i++,j++;
    return hashsum[j]-hashsum[i-1]*pw[j-i+1];
}