Create CountingSort.java

java/CountingSort.java

@@ -0,0 +1,44 @@
+import java.util.Arrays;
+
+public class CountingSort {
+
+	public static void main(String[] args) {
+		int[] arr = { 2, 4, 3, 1 };
+
+		System.out.println(Arrays.toString(arr)); 
+		int[] sortedArr = countingSort(arr);
+		System.out.println(Arrays.toString(sortedArr)); 
+	}
+	private static int[] countingSort(int[] arr) {
+
+		int max = findMax(arr);
+		if (max == Integer.MIN_VALUE) {
+			return new int[] {};
+		}
+		int[] counts = new int[max + 1];
+		for (int num : arr) {
+			counts[num]++;
+		}
+		for (int idx = 1; idx < counts.length; idx++) {
+			counts[idx] = counts[idx - 1] + counts[idx];
+		}
+		int[] sortedArray = new int[arr.length];
+		int current, sortedIdx;
+		for (int idx = arr.length - 1; idx >= 0; idx--) {
+			current = arr[idx];
+			counts[current]--;
+			sortedIdx = counts[current];
+			sortedArray[sortedIdx] = current;
+		}
+		return sortedArray;
+	}
+	private static int findMax(int[] arr) {
+		int max = Integer.MIN_VALUE;
+		for (int num : arr) {
+			if (num > max) {
+				max = num;
+			}
+		}
+		return max;
+	}
+}