Add Counting Sort - java (#124)

* Add CountingSort.java

* File name and Readme sorting

* static main and print array

sorting/README.md

@@ -37,6 +37,7 @@
 3. [Selection Sort](java/selection-sort.java)
 4. [Merge Sort](java/merge-sort.java)
 5. [Quick Sort](java/quick-sort.java)
+6. [Counting Sort](java/counting-sort.java)
 
 ### JavaScript
 

sorting/java/counting-sort.java

@@ -0,0 +1,74 @@
+public class CountingSort {
+
+    /**
+     * Public method to use the counting sort algortithm
+     * @param arr - the array in input
+     */
+    public void sort(int[] arr){
+
+        int[] sortedArray = new int[arr.length + 1];
+
+        // Search max element
+        int max = arr[0];
+        for(int i = 0; i < arr.length; i++){
+            if(arr[i] > max){
+                max = arr[i];
+            }
+        }
+
+        // Create counting array
+        int[] countArray = new int[max + 1];
+        for(int i = 0; i < countArray.length; i++){
+            countArray[i] = 0;
+        }
+
+        // Count elements in array
+        for(int i = 0; i < arr.length; i++){
+            countArray[arr[i]]++;
+        }
+
+
+        for(int i = 1; i < countArray.length; i++){
+            countArray[i] += countArray[i - 1];
+        }
+
+        for (int i = arr.length - 1; i >= 0; i--) {
+            sortedArray[countArray[arr[i]] - 1] = arr[i];
+            countArray[arr[i]]--;
+        }
+
+        System.arraycopy(sortedArray, 0, arr, 0, arr.length);
+    }
+
+    /**
+     * Main method for testing
+     * @param args
+     */
+    public static void main(String[] args) throws Exception {
+        CountingSort count = new CountingSort();
+
+        int[] test = {1,9,8,7,6,5,4,3,2,12,546,23,123,5768,689,45,6342,0,76,856,34,412,12,32,353,46,568,456,234,3456,467,345345,345,345,};
+
+        count.sort(test);
+
+        for(int i = 1; i < test.length; i++){
+            if(test[i] < test[i - 1]){
+                throw new Exception("[ERROR] Ops! Counting sort not work!");
+            }
+        }
+
+        printArray(test);
+    }
+
+    /**
+     * Print an array
+     * @param arr
+     */
+    public static void printArray(int[] arr){
+
+        System.out.println("Sorted array: ");
+        for(int i = 0; i < arr.length; i++){
+           System.out.println(" " + i);
+        }
+    }
+}