ProEuler P_010a

package problems;

public class Problem_010a {

    /**
     *Find the sum of all the primes below two million.
     */

    /* Pseudocode: To find the sum of all the primes below two million.
     *
     * 1. Start looking for primes, start with prime nr. 3 and increment by two. (Use while loop)
     *  1a. In the primetest, only test with previously found primes.
     *  1b. In the primetest, only test numbers that are smaller than the square root of the number.
     * 2. When a prime is found check if its smaller than two million.
     * 3. If it is smaller.
     *  3a. Store it in the array.
     *  3b. Add it to the SUM variable.
     *
     *
     * */

    public static void main(String[] args) {

            System.out.println("Declaring variables...");

            final long start = 3;
            final long end = 100000;

            int primeCounter = 1;

            int arrayChecks = 0;
            int trialDivChecks = 0;

            long prime = 0;
            long primeSum = 2;
            long testrange = 100000;

            long[] anArray;              // declares an array of integers



            anArray = new long[100000];
            anArray[1] = 2;





            System.out.println("Starting computation...\n");
            System.out.println("Testing odd numbers less than: " +testrange);

            System.out.println("\nINFO: We have stored " +primeCounter +" primes, because we already know 2 is a prime. \n");

            // START TESTING


            for (long number = start; number <= end; number += 2) {

                    if (number > testrange) {   // Stop testing for primes when the prime candidate is over 50.
                            break;
                    }



                    trialDivChecks -= trialDivChecks;   // Reset test counters



                 //   System.out.println("For loop is now testing: " +number +" \n");  // What number are you testing?
                    if( primeCounter % 1000 == 0){
                    System.out.println("INFO: Stored " +primeCounter +" primes in our array to check. Sum is up to: " +primeSum +" and latest prime is: " +number);
                    }
                     // prime array starts over here if number is divisble by number in array

                    for (long i = 1; i <= number; i +=2) {  // Prime tester starts

                        arrayChecks -= arrayChecks;
                 //     System.out.println("**Just before OUT label.**");
                        out:

                                for(int arrayIndex = 1; arrayIndex <= primeCounter; arrayIndex++){  // For loop containing an ArrayCheck and modulo check

                                    arrayChecks++;


                                //  System.out.println("Running IF statement on array...");
                            //      System.out.println("Checking if " +number +" is divisble by the stored prime " +anArray[arrayIndex] +".");


                                    if (number % anArray[arrayIndex] == 0){ // Is prime stored in the array at index J is a factor of the number?
                                //      System.out.println("Number divisble by previous prime!:" + anArray[arrayIndex]);
                            //          System.out.println("Number of checks in Array?: " + arrayChecks +"\n");
                                        break out;                                                              // Yes it is, so stop running the FOR loop.
                                    } else if ( arrayChecks == arrayIndex+1){
                                        break out;
                                    }
                                //  System.out.println(number + " is not divisble by " +anArray[arrayIndex] +".");

                                //  System.out.println("");



                                    if (arrayIndex == primeCounter && i == number ){

                          //                  System.out.println("Starting trial division...");

                                            if (number % i == 0) {  // Trial Division Check STARTS
                                                trialDivChecks ++;
                                                    if (i == number) {

                                //                          System.out.print(number + " is prime");
                                                            primeCounter++;
                                                            prime = number;
                                                            anArray[primeCounter] = prime;
                        //                                    System.out.println(", stored! \n");
                                                            primeSum += prime;

                        //                                    System.out.println("Number of primes found and stored so far: " +primeCounter);

                                                    }
                      //                              System.out.println("Number of checks by trial?: " + trialDivChecks +"\n");
                                                    break out;
                                            }
                                    }




                                } // PrimeyArray Check ENDS




                    }

            }


                    System.out.println("Last Prime is Nr. " + primeCounter + ": " + anArray[primeCounter]);
                    System.out.println("Sum of primes: " + primeSum);

                    System.out.println();


                    }


    }