Merge branch 'master' of git://github.com/laucer/java-algorithms-implementation into laucer-master

Author: phishman3579

Permutations.java

@@ -0,0 +1,60 @@
+package com.jwetherell.algorithms.mathematics;
+
+import java.util.LinkedList;
+
+
+/*
+ * Recursive permutations generating
+ * @author Lucjan Roslanowski <lucjanroslanowski@gmail.com>
+ * 
+ * Example of usage:
+ * int numbers[] = {7,5,3};
+ * LinkedList<LinkedList<Integer>> result = new LinkedList<LinkedList<Integer>>();
+ * getAllPermutations(numbers,result);
+ */
+
+public class Permutations {	
+	
+	public static LinkedList<LinkedList<Integer>> getAllPermutations(final int[] numbers,  LinkedList<LinkedList<Integer>> result){
+		//numbers given in an array are also a permutation
+		LinkedList<Integer> firstPermutation = new LinkedList<>();
+		for(int el : numbers){
+			firstPermutation.add(new Integer(el));
+		}
+		result.add(firstPermutation);
+		//let's permute all elements in array starting from index 0
+		return permute(numbers, 0, result);
+	}
+	
+	public static LinkedList<LinkedList<Integer>> permute(final int[] numbers, 
+			int currentElementIndex,  LinkedList<LinkedList<Integer>> result){
+		if(currentElementIndex == numbers.length - 1){
+			return result;
+		}
+		
+		for(int i = currentElementIndex; i < numbers.length; ++i){
+			//swapping two elements
+			int temp = numbers[i];
+			numbers[i] = numbers[currentElementIndex];
+			numbers[currentElementIndex] = temp;
+			
+			permute(numbers, currentElementIndex + 1,result);
+			
+			//all next permutation found
+			if(i != currentElementIndex){
+				LinkedList<Integer> nextPermutation = new LinkedList<>();
+				for(int j = 0; j < numbers.length; j++)
+					nextPermutation.add(new Integer(numbers[j]));
+				result.add(nextPermutation);
+			}
+			
+			//swapping back two elements 
+			temp = numbers[i];
+			numbers[i] = numbers[currentElementIndex];
+			numbers[currentElementIndex] = temp;
+		}	
+		return result;
+	}
+	
+	
+}

test/com/jwetherell/algorithms/mathematics/test/PermutationsTest.java

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+package com.jwetherell.algorithms.mathematics.test;
+
+import com.jwetherell.algorithms.mathematics.Permutations;
+import static org.junit.Assert.*;
+
+import java.util.LinkedList;
+
+import org.junit.Test;
+
+public class PermutationsTest {
+
+	@Test
+	public void test1NumberOfPermutations() {
+		int numbers[] = {1,2,3,4};
+		int expectedNumberOfPermutations = 24;
+		LinkedList<LinkedList<Integer>> result = new LinkedList<LinkedList<Integer>>();
+		
+		assertEquals(expectedNumberOfPermutations, (Permutations.getAllPermutations(numbers,result)).size());
+	}
+	
+	@Test
+	public void test2NumberOfPermutations() {
+		int numbers[] = {3,4,2};
+		int expectedNumberOfPermutations = 6;
+		LinkedList<LinkedList<Integer>> result = new LinkedList<LinkedList<Integer>>();
+		
+		assertEquals(expectedNumberOfPermutations, (Permutations.getAllPermutations(numbers,result)).size());
+	}
+	
+	@Test
+	public void test3NumberOfPermutations() {
+		int numbers[] = {3,4,2,5,4,9};
+		int expectedNumberOfPermutations = 720;
+		LinkedList<LinkedList<Integer>> result = new LinkedList<LinkedList<Integer>>();
+		
+		assertEquals(expectedNumberOfPermutations, (Permutations.getAllPermutations(numbers,result)).size());
+	}
+	
+	@Test
+	public void testComparePermutations() {
+		int numbers[] = {4,2};
+		
+		LinkedList<Integer> firstPermutation = new LinkedList<>();
+		firstPermutation.add(4);
+		firstPermutation.add(2);
+		
+		LinkedList<Integer> secondPermutation = new LinkedList<>();
+		secondPermutation.add(2);
+		secondPermutation.add(4);
+		
+		LinkedList<LinkedList<Integer>> allPermutations = new LinkedList<LinkedList<Integer>>();
+		allPermutations.add(firstPermutation);
+		allPermutations.add(secondPermutation);
+		
+		LinkedList<LinkedList<Integer>> result = new LinkedList<LinkedList<Integer>>();
+		
+		assertEquals(allPermutations, Permutations.getAllPermutations(numbers,result));
+	}
+}