Added example to find permutation of numbers in array

YogenRaii · YogenRaii · commit acabaa8eac1c · 2019-06-21T21:18:34.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/Permutations.java b/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/Permutations.java
@@ -0,0 +1,51 @@
+package com.eprogrammerz.examples.algorithm.crackingCoding;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Find permutations of list of numbers
+ */
+public class Permutations {
+    public List<List<Integer>> findPermutations(List<Integer> num) {
+        List<List<Integer>> permutations = new ArrayList<>();
+        findPermutations(num, new ArrayList<>(), permutations);
+        return permutations;
+    }
+
+    private void findPermutations(List<Integer> nums, List<Integer> permutation, List<List<Integer>> permutations) {
+        if (nums.size() == 0) {
+            permutations.add(new ArrayList<>(permutation));
+        } else {
+            for (int i = 0; i < nums.size(); i++) {
+                List<Integer> remaining1 = nums.subList(0, i);
+                List<Integer> remaining2 = nums.subList(i + 1, nums.size());
+                permutation.add(nums.get(i));
+
+                List<Integer> remaining = new ArrayList<>();
+                remaining.addAll(remaining1);
+                remaining.addAll(remaining2);
+                findPermutations(remaining, permutation, permutations);
+                permutation.remove(nums.get(i));
+            }
+        }
+    }
+
+    @Test
+    public void testFindDenomination() {
+        List<List<Integer>> actual = findPermutations(Arrays.asList(1, 2, 3));
+        List<Integer> p1 = Arrays.asList(1, 2, 3);
+        List<Integer> p2 = Arrays.asList(1, 3, 2);
+        List<Integer> p3 = Arrays.asList(2, 1, 3);
+        List<Integer> p4 = Arrays.asList(2, 3, 1);
+        List<Integer> p5 = Arrays.asList(3, 1, 2);
+        List<Integer> p6 = Arrays.asList(3, 2, 1);
+        List<List<Integer>> expected = Arrays.asList(p1, p2, p3, p4, p5, p6);
+        assertEquals(expected, actual);
+    }
+}
