Merge pull request #1450 from shellhub/dev-1

Updated BucketSort

Sorts/BucketSort.java

@@ -1,72 +1,115 @@
 package Sorts;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 import java.util.Random;
- 
-public class BucketSort 
-{
-    static int[] sort(int[] sequence, int maxValue) 
-    {
-        // Bucket Sort
-        int[] Bucket = new int[maxValue + 1];
-        int[] sorted_sequence = new int[sequence.length];
- 
-        for (int i = 0; i < sequence.length; i++)
-            Bucket[sequence[i]]++;
- 
-        int outPos = 0;
-        for (int i = 0; i < Bucket.length; i++)
-            for (int j = 0; j < Bucket[i]; j++)
-                sorted_sequence[outPos++] = i;
- 
-        return sorted_sequence;
-    }
- 
-    static void printSequence(int[] sorted_sequence) 
-    {
-        for (int i = 0; i < sorted_sequence.length; i++)
-            System.out.print(sorted_sequence[i] + " ");
-    }
- 
-    static int maxValue(int[] sequence) 
-    {
-        int maxValue = 0;
-        for (int i = 0; i < sequence.length; i++)
-            if (sequence[i] > maxValue)
-                maxValue = sequence[i];
-        return maxValue;
-    }
- 
-    public static void main(String args[]) 
-    {
-        System.out.println("Sorting of randomly generated numbers using BUCKET SORT");
+
+/**
+ * Wikipedia: https://en.wikipedia.org/wiki/Bucket_sort
+ */
+public class BucketSort {
+    public static void main(String[] args) {
+        int[] arr = new int[10];
+
+        /* generate 10 random numbers from -50 to 49 */
         Random random = new Random();
-        int N = 20;
-        int[] sequence = new int[N];
- 
-        for (int i = 0; i < N; i++)
-            sequence[i] = Math.abs(random.nextInt(100));
- 
-        int maxValue = maxValue(sequence);
- 
-        System.out.println("\nOriginal Sequence: ");
-        printSequence(sequence);
- 
-        System.out.println("\nSorted Sequence: ");
-        printSequence(sort(sequence, maxValue));
+        for (int i = 0; i < arr.length; ++i) {
+            arr[i] = random.nextInt(100) - 50;
+        }
+
+        bucketSort(arr);
+
+        /* check array is sorted or not */
+        for (int i = 0, limit = arr.length - 1; i < limit; ++i) {
+            assert arr[i] <= arr[i + 1];
+        }
+    }
+
+    /**
+     * BucketSort algorithms implements
+     *
+     * @param arr the array contains elements
+     */
+    private static void bucketSort(int[] arr) {
+        /* get max value of arr */
+        int max = max(arr);
+
+        /* get min value of arr */
+        int min = min(arr);
+
+        /* number of buckets */
+        int numberOfBuckets = max - min + 1;
+
+        List<List<Integer>> buckets = new ArrayList<>(numberOfBuckets);
+
+        /* init buckets */
+        for (int i = 0; i < numberOfBuckets; ++i) {
+            buckets.add(new ArrayList<>());
+        }
+
+        /* store elements to buckets */
+        for (int value : arr) {
+            int hash = hash(value, min, numberOfBuckets);
+            buckets.get(hash).add(value);
+        }
+
+        /* sort individual bucket */
+        for (List<Integer> bucket : buckets) {
+            Collections.sort(bucket);
+        }
+
+        /* concatenate buckets to origin array */
+        int index = 0;
+        for (List<Integer> bucket : buckets) {
+            for (int value : bucket) {
+                arr[index++] = value;
+            }
+        }
+    }
+
+
+    /**
+     * Get index of bucket which of our elements gets placed into it.
+     *
+     * @param elem           the element of array to be sorted
+     * @param min            min value of array
+     * @param numberOfBucket the number of bucket
+     * @return index of bucket
+     */
+    private static int hash(int elem, int min, int numberOfBucket) {
+        return (elem - min) / numberOfBucket;
+    }
+
+    /**
+     * Calculate max value of array
+     *
+     * @param arr the array contains elements
+     * @return max value of given array
+     */
+    public static int max(int[] arr) {
+        int max = arr[0];
+        for (int value : arr) {
+            if (value > max) {
+                max = value;
+            }
+        }
+        return max;
+    }
+
+    /**
+     * Calculate min value of array
+     *
+     * @param arr the array contains elements
+     * @return min value of given array
+     */
+    public static int min(int[] arr) {
+        int min = arr[0];
+        for (int value : arr) {
+            if (value < min) {
+                min = value;
+            }
+        }
+        return min;
     }
 }
-
-
-/*
-#Output:
-
-$ javac Bucket_Sort.java
-$ java Bucket_Sort
- 
-Sorting of randomly generated numbers using BUCKET SORT
- 
-Original Sequence: 
-95 9 95 87 8 81 18 54 57 53 92 15 38 24 8 56 29 69 64 66 
-Sorted Sequence: 
-8 8 9 15 18 24 29 38 53 54 56 57 64 66 69 81 87 92 95 95
-*/