45 lines
1.5 KiB
Java
45 lines
1.5 KiB
Java
package com.jwetherell.algorithms.sequence;
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/**
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* Compute the result of adding a sequence of numbers from N (startNumber) to N+X (startNumber+numberOfNumbersToCompute)
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* <p>
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* https://en.wikipedia.org/wiki/Arithmetic_progression
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* <br>
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* @author Justin Wetherell <phishman3579@gmail.com>
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*/
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public class ArithmeticProgression {
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/**
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* Compute the result of adding X (numberOfNumbersToCompute) together starting at N (startNumber).
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* <p>
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* e.g. result = N + (N+1) + (N+2) + (N+3) + ..... + (N+X)
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*/
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public static final long sequenceTotalUsingLoop(int startNumber, int numberOfNumbersToCompute) {
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int start = startNumber;
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int length = numberOfNumbersToCompute;
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long result = 0L;
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while (length > 0) {
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result += start++;
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length--;
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}
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return result;
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}
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/**
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* Compute the result of adding X (numberOfNumbersToCompute) together starting at N (startNumber) using triangular numbers.
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* <p>
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* e.g. result = N + (N+1) + (N+2) + (N+3) + ..... + (N+X)<br>
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* <br>
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* https://en.wikipedia.org/wiki/Triangular_number
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*/
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public static final long sequenceTotalUsingTriangularNumbers(int startNumber, int numberOfNumbersToCompute) {
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// n*(n+1)/2
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final int start = startNumber;
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final int length = numberOfNumbersToCompute;
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long result = length * (length + 1) / 2;
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result += (start - 1) * length;
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return result;
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}
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}
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