46 lines
1.4 KiB
Java
46 lines
1.4 KiB
Java
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package ProjectEuler;
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/**
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* The sum of the squares of the first ten natural numbers is,
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* 1^2 + 2^2 + ... + 10^2 = 385
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* The square of the sum of the first ten natural numbers is,
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* (1 + 2 + ... + 10)^2 = 552 = 3025
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* Hence the difference between the sum of the squares of the first ten natural
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* numbers and the square of the sum is 3025 − 385 = 2640.
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* Find the difference between the sum of the squares of the first N natural
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* numbers and the square of the sum.
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* <p>
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* link: https://projecteuler.net/problem=6
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*/
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public class Problem06 {
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public static void main(String[] args) {
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int[][] testNumbers = {
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{10, 2640},
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{15, 13160},
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{20, 41230},
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{50, 1582700}
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};
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for (int[] testNumber : testNumbers) {
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assert solution1(testNumber[0]) == testNumber[1]
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&& solutions2(testNumber[0]) == testNumber[1];
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}
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}
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private static int solution1(int n) {
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int sum1 = 0;
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int sum2 = 0;
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for (int i = 1; i <= n; ++i) {
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sum1 += i * i;
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sum2 += i;
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}
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return sum2 * sum2 - sum1;
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}
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private static int solutions2(int n) {
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int sumOfSquares = n * (n + 1) * (2 * n + 1) / 6;
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int squareOfSum = (int) Math.pow((n * (n + 1) / 2.0), 2);
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return squareOfSum - sumOfSquares;
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}
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}
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