using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CSEP521 {
    public class HashCounter {

        const uint P1 = 4294967291;  // prime less than 2^32
        const uint P2 = 65521;       // prime less than 2^16
        int B;
        int[] count;

        const uint CW_P = 2147483629;  // prime less than 2^31
        uint CW_A;
        uint CW_B;

        public HashCounter(int b, Random rand) {
            B = b;
            count = new int[B];
            for (int i = 0; i < B; i++)
                count[i] = 0;

            CW_A = (uint) rand.Next(1, (int) CW_P);
            CW_B = (uint) rand.Next(1, (int) CW_P);

        }

        public void Count(string str) {
            count[Hash(str)]++;
        }

        public int LookupVal(string str) {
            return count[Hash(str)];
        }


        // Compress the string to an unsigned int,  and then use a C-W hash, then mod table size
        uint Hash(string str) {

            ulong val = HashString(str);

            ulong result = (val * CW_A + CW_B) % CW_P;

            return (uint)(result % (uint) B);
        }

        // evaluate a polynomial with the characters as coefficients
        uint HashString(string str) {
            ulong result = 0;

            ulong x = 1;

            for (int i = 0; i < str.Length; i++) {
                ulong c = (ulong) str[i];
                result = (result + c * x) % P1;
                x = (x * P2) % P1;


            }

            return (uint) result;

        }

        public override string ToString() {
            return Algorithm.ArrayToString(count);
        }
    }
}