51 lines
1.2 KiB
Java
51 lines
1.2 KiB
Java
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package ProjectEuler;
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/**
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* If we list all the natural numbers below 10 that are multiples of 3 or 5,
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* we get 3, 5, 6 and 9. The sum of these multiples is 23.
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* <p>
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* Find the sum of all the multiples of 3 or 5 below 1000.
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* <p>
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* Link: https://projecteuler.net/problem=1
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*/
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public class Problem01 {
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public static void main(String[] args) {
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int[][] testNumber = {
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{3, 0},
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{4, 3},
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{10, 23},
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{1000, 233168},
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{-1, 0}
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};
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for (int[] ints : testNumber) {
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assert solution1(ints[0]) == ints[1];
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assert solution2(ints[0]) == ints[1];
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}
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}
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private static int solution1(int n) {
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int sum = 0;
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for (int i = 3; i < n; ++i) {
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if (i % 3 == 0 || i % 5 == 0) {
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sum += i;
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}
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}
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return sum;
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}
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private static int solution2(int n) {
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int sum = 0;
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int terms = (n - 1) / 3;
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sum += terms * (6 + (terms - 1) * 3) / 2;
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terms = (n - 1) / 5;
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sum += terms * (10 + (terms - 1) * 5) / 2;
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terms = (n - 1) / 15;
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sum -= terms * (30 + (terms - 1) * 15) / 2;
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return sum;
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}
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}
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