BubbleSort: Fix to reduce number of iterations for sorted array as input (blakeembrey#168)

Previous solution performed `O(N ^ 2)` iterations for sorted input. This fixes it by exiting loop if array is already sorted and performs at most `O(N)` iterations in this case.

Author: jayeshcp

solutions/java/BubbleSort.java

@@ -3,17 +3,23 @@
  * compares each pair of adjacent items and swaps them if they are in the wrong order. 
  * The pass through the list is repeated until no swaps are needed, which indicates that the list is sorted.
  * Author : Viveka Aggarwal
+ * Author : Jayesh Chandrapal
  */
 
-public class bubbleSort {
+public class BubbleSort {
 	public static void sort(int[] arr) {
-		int n = arr.length-2;
-		while(n > 0) {
-			for(int j = 0 ; j <= n ; j++) {
-				if(arr[j] >= arr[j+1])
-					swap(j, j+1, arr);
+		int len = arr.length;
+    boolean unsorted = true;
+        
+		while(unsorted) {
+      unsorted = false;
+            
+			for(int j = 0 ; j < len - 1; j++) {
+        if(arr[j] > arr[j + 1]) {
+				  swap(j, j + 1, arr);
+          unsorted = true;
+        }
 			}
-			n--;
 		}
 	}
 
@@ -24,8 +30,11 @@ public static void swap(int a, int b, int[] arr) {
 	}
 
 	public static void main(String[] a) {
-		int[] arr = {23, 3, 12, 54, 34, 77, 78, 87, 92, 12};
+		int[] arr = {23, 3, 12, 54, 34, 77, 78, 87, 92, 12};  // unsorted input
+		//int[] arr = {3,12, 12, 23, 34, 54, 77, 78, 87, 92};   // sorted input
+		
 		sort(arr);
+		
 		for(int i : arr) {
 			System.out.print(i + " ");
 		}

solutions/python/bubble-sort.py

@@ -1,13 +1,31 @@
+import unittest
 
 def bubblesort(lst):
-	for i in range(0,len(lst)-1):
-		for j in range(i+1,len(lst)):
-			if lst[i]>lst[j]:
-				temp=lst[i]
-				lst[i]=lst[j]
-				lst[j]=temp
+	for i in range(0, len(lst) - 1):
+		for j in range(i + 1, len(lst)):
+			if lst[i] > lst[j]:
+                # swap values
+				lst[i], lst[j] = lst[j], lst[i]
 	return lst
-	
-l=[1,4,2,4,6,2,6,8,5,8,9,5]
-for i in bubblesort(l):
-	print (i)
+
+class Test(unittest.TestCase):
+    def testUnsortedSmall(self):
+        self.assertEqual([1,2,3,4], bubblesort([4,3,2,1]))
+
+    def testSortedSmall(self):
+        self.assertEqual([1,2,3,4], bubblesort([1,2,3,4]))
+
+    def testUnsortedLarge(self):
+        self.assertEqual([1,2,3,4,5,6,7,8,9,10], bubblesort([6,3,4,8,7,9,5,10,1,2]))
+
+    def testSortedLarge(self):
+        self.assertEqual([1,2,3,4,5,6,7,8,9,10], bubblesort([1,2,3,4,5,6,7,8,9,10]))
+
+    def testSingleInput(self):
+        self.assertEqual([1], bubblesort([1]))
+
+    def testBlankInput(self):
+        self.assertEqual([], bubblesort([]))
+
+if __name__ == '__main__':
+    unittest.main()