feat(day 117): implement symmetric difference with duplicate filtering and stable ordering

Author: JohnSunny21

FreeCodeCamp/CodingQ/SymmetricDifference.py

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+"""
+Symmetric Difference
+Given two arrays, return a new array containing the symmetric difference of them.
+
+The symmetric difference between two sets is the set of values that appear in either set, but not both.
+Return the values in the order they first appear in the input arrays.
+
+
+"""
+
+import unittest
+
+class SymmetricDifferenceTest(unittest.TestCase):
+
+    def test1(self):
+        self.assertEqual(difference([1, 2, 3], [3, 4, 5]), [1, 2, 4, 5])
+
+    def test2(self):
+        self.assertEqual(difference(["a", "b"],["c", "b"]),["a", "c"])
+
+    def test3(self):
+        self.assertEqual(difference([1, "a", 2],[2, "b", "a"]), [1, "b"])
+
+    def test4(self):
+        self.assertEqual(difference([1, 3, 5, 7, 9],[1, 2, 3, 4, 5, 6, 7, 8, 9]),[2, 4, 6, 8])
+
+def difference(arr1, arr2):
+    """
+    The Limitations for this approach are
+    The block of code will include duplicates if the same unique item appears multiple times in 
+    one array but not in the other.
+    example:
+        print(difference([1, 1, 2],[2, 3]))
+        # Output: [1, 1, 3] ( but expected [1, 3])
+
+    1. Because both 1's from arr1 get appended.
+    2. Efficiency : Each item not in arr2 check is an O(n) membership test on a list. For large arrays, this become slow.
+    Using sets would be faster.
+
+    """
+
+    result = []
+
+    for item in arr1:
+        if item not in arr2:
+            result.append(item)
+
+    for item in arr2:
+        if item not in arr1:
+            result.append(item)
+
+    return result
+
+def difference(arr1, arr2):
+    result = []
+    seen = set()
+
+    for item in arr1:
+        if item not in arr2 and item not in seen:
+            result.append(item)
+            seen.add(item)
+
+    for item in arr2:
+        if item not in arr1 and item not in seen:
+            result.append(item)
+            seen.add(item)
+
+
+    return result
+
+
+
+
+
+
+if __name__ == "__main__":
+    print(difference([1,1,3], [2, 3, 5]))
+    # unittest.main()