hash和hsah表

一维hash
$$
eg: S= "a ,b, c" ;
$$
$$
hash(S)=1p^2+2p+3;
$$

unsigned long long p=13331;
unsigned long long hash()
{cin>>a;int l=strlen(a);int res=0;for(int i=0;i<l;i++){res=(res*p+a[i]);}return res;
}

二维hash
总共hash两次，一次横向，一次竖向；

unsigned long long hash()
{for(int i=1;i<=n;i++){for(int j=1;j<=n;j++){hsh[i][j]=hsh[i][j-1]*p_1+a[i][j];}}for(int i=1;i<=n;i++){for(int j=1;j<=n;j++){hsh[i][j]+=hsh[i-1][j]*p_2;}}
}

左上角$（x,y)$右下$（x_1,y_1)$矩阵$hash$值为：

$$
hash(x_1,y_1)-hsah(x-1,y1)*p_2 ^{x_1-x+1}-hash(x_1,y-1)
$$
$$
p_1^{{y_1-y+1}+hash(x-1,y-1)*p_2}p_1^{y_1-y+1}
$$