Add algorithm that tests knowledge of strings (keon#234)

* Add a function that validates latitude and longitude.

* Update README.md by adding validate_coordinates.py

* Fix indentation error

* Fix indentation errors and follow PEP8

* Add import statement for unittest

* Fix function names

* Add delete_reocurring_characters

* Update README.md by adding delete_reoccuring_char

* Add PR review changes

README.md

@@ -188,7 +188,9 @@ To run the tests, clone the repo and run :
     - [remove_min](stack/remove_min.py)
     - [is_sorted](stack/is_sorted.py)
 - [strings](strings)
+    - [delete_reoccurring_characters](strings/delete_reoccurring_characters.py)
     - [strip_url_params](strings/strip_url_params.py)
+    - [validate_coordinates](strings/validate_coordinates.py)
     - [domain_extractor](strings/domain_extractor.py)
     - [merge_string_checker](strings/merge_string_checker.py)
     - [add_binary](strings/add_binary.py)

strings/delete_reoccurring.py

@@ -0,0 +1,19 @@
+"""
+QUESTION: Given a string as your input, delete any reoccurring 
+character, and return the new string.
+
+This is a Google warmup interview question that was asked duirng phone screening
+at my university. 
+"""
+
+# time complexity O(n)
+def delete_reoccurring_characters(string):
+    seen_characters = set()
+    output_string = ''
+    for char in string:
+        if char not in seen_characters:
+            seen_characters.add(char)
+            output_string += char
+    return output_string
+
+

strings/validate_coordinates.py

@@ -0,0 +1,67 @@
+""""
+Create a function that will validate if given parameters are valid geographical coordinates.
+Valid coordinates look like the following: "23.32353342, -32.543534534". The return value should be either true or false.
+Latitude (which is first float) can be between 0 and 90, positive or negative. Longitude (which is second float) can be between 0 and 180, positive or negative.
+Coordinates can only contain digits, or one of the following symbols (including space after comma) -, .
+There should be no space between the minus "-" sign and the digit after it.
+
+Here are some valid coordinates:
+-23, 25
+43.91343345, 143
+4, -3
+
+And some invalid ones:
+23.234, - 23.4234
+N23.43345, E32.6457
+6.325624, 43.34345.345
+0, 1,2
+
+"""
+# I'll be adding my attempt as well as my friend's solution (took us ~ 1 hour)
+
+# my attempt
+import re
+def is_valid_coordinates_0(coordinates):
+    for char in coordinates:
+        if not (char.isdigit() or char in ['-', '.', ',', ' ']):
+            return False
+    l = coordinates.split(", ")
+    if len(l) != 2:
+        return False
+    print(l)
+    try:
+        latitude = float(l[0])
+        longitude = float(l[1])
+    except:
+        return False
+    print(latitude, longitude)
+    return -90 <= latitude <= 90 and -180 <= longitude <= 180
+
+# friends solutions
+def is_valid_coordinates_1(coordinates):
+    try:
+        lat, lng = [abs(float(c)) for c in coordinates.split(',') if 'e' not in c]
+    except ValueError:
+        return False
+
+    return lat <= 90 and lng <= 180
+
+# using regular expression
+def is_valid_coordinates_regular_expression(coordinates):
+    return bool(re.match("-?(\d|[1-8]\d|90)\.?\d*, -?(\d|[1-9]\d|1[0-7]\d|180)\.?\d*$", coordinates))  
+
+import unittest
+class TestSuite(unittest.TestCase):
+	def test_valid(self):
+		valid_coordinates = ["-23, 25","4, -3","90, 180","-90, -180"]
+		for coordinate in valid_coordinates:
+			self.assertTrue(is_valid_coordinates_0(coordinate))
+
+	def test_invalid(self):
+		invalid_coordinates = ["23.234, - 23.4234","99.234, 12.324","6.325624, 43.34345.345","0, 1,2","23.245, 1e1"]
+		for coordinate in invalid_coordinates:
+			self.assertFalse(is_valid_coordinates_0(coordinate))
+
+
+if __name__ == "__main__":
+    unittest.main()