get Lowest Common Denominator - Java java.lang

Java examples for java.lang:int prime

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Description

get Lowest Common Denominator

Demo Code


import java.util.List;

public class Main{
    /**//www  .  j  av  a2  s  . c  om
     * @param fractions
     * @return
     */
    public static int getLowestCommonDenominator(List<Pair> fractions) {
        int max = 0;
        for (Pair pair : fractions) {
            if (pair.getB() > max) {
                max = pair.getB();
            }
        }

        int[] primeList = PrimeUtil.getAllPrimeBelowN(max);
        int[][] allPrimeExp = new int[fractions.size()][primeList.length];
        int index = 0;
        for (Pair pair : fractions) {
            int number = pair.getB();
            for (int i = 1; i < primeList.length && primeList[i] <= number; i++) {
                if (number % primeList[i] == 0) {
                    int temp = number;
                    int exp = 0;
                    while (temp % primeList[i] == 0) {
                        exp++;
                        temp = temp / primeList[i];
                    }

                    allPrimeExp[index][i] = exp;
                }
            }
            index++;
        }

        int[] primeExp = new int[primeList.length];
        for (int i = 1; i < primeList.length; i++) {
            int maxExp = 0;
            for (int j = 0; j < fractions.size(); j++) {
                if (allPrimeExp[j][i] > maxExp) {
                    maxExp = allPrimeExp[j][i];
                }
            }
            primeExp[i] = maxExp;
        }

        int result = 1;
        for (int i = 1; i < primeList.length; i++) {
            result *= Math.pow(primeList[i], primeExp[i]);
        }

        return result;

    }
    /**
     * return prime list equal or below n
     * Please notice that element 0 is kept for 1 although 1 is not prime, this is preserved for usage in special occasions
     * 
     * @param n
     * @return
     */
    public static int[] getAllPrimeBelowN(int n) {
        if (n == 1) {
            return new int[] { 1 };
        }

        int[] temp = new int[n];
        boolean[] flags = new boolean[n + 1];

        temp[0] = 1;
        temp[1] = 2;
        int index = 2;

        int lastPrime = 2;
        while (lastPrime < n) {
            for (int i = 2; i * lastPrime <= n; i++) {
                flags[i * lastPrime] = true;
            }

            boolean found = false;
            for (int i = lastPrime + 1; i <= n; i++) {
                if (!flags[i]) {
                    found = true;
                    lastPrime = i;
                    temp[index++] = lastPrime;
                    break;
                }
            }

            if (!found) {
                break;
            }
        }

        int[] result = new int[index];
        System.arraycopy(temp, 0, result, 0, index);
        return result;

    }
}

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