add 1.6_string_compression.py

Author: bap2pecs0

Cracking_the_coding_interview/v6/1.6_string_compression.py

@@ -0,0 +1,99 @@
+'''Question:
+Implement a method to perform basic string compression using the counts of 
+repeated characters. For example, the string aabcccccaaa would become a2b1c5a3. 
+
+If the "compressed" string would not become smaller than the original string, 
+your method should return the original string. 
+
+You can assume the string has only uppercase and lowercase letters (a - z).
+'''
+
+import unittest
+from test_utils import UnitTestBase
+
+# time: O(n)
+# space: O(n)
+def str_comp(s):
+  if s == '':
+    return ''
+
+  cur, ct, res = s[0], 0, ''
+  for c in s:
+    if c == cur:
+      ct +=1
+    else:
+      # Note: res = res + cur + str(ct) will be very slow and result in not O(n)
+      res += cur + str(ct)
+      cur, ct = c, 1
+  res += cur + str(ct)
+
+  # another way to write it: min(s, res, key=len)
+  return res if len(res) < len(s) else s
+
+class TestStrComp(UnitTestBase, unittest.TestCase):
+  def data_provider(self):
+    return [
+      ('', ''), # 0
+      ('a', 'a'), # 1
+      ('aa', 'aa'), # 2
+      ('aaa', 'a3'), # 3
+      ('aaaa', 'a4'), # 4
+
+      ('ab', 'ab'), # 11
+      ('abb', 'abb'), # 12
+      ('abbb', 'abbb'), # 13
+      ('abbbb', 'a1b4'), #14
+      ('aab', 'aab'), # 21
+      ('aabb', 'aabb'), # 22
+      ('aabbb', 'a2b3'), # 23
+      ('aabbbb', 'a2b4'), # 24
+      ('aaab', 'aaab'), # 31
+      ('aaabb', 'a3b2'), # 32
+      ('aaabbb', 'a3b3'), # 33
+      ('aaabbbb', 'a3b4'), # 34
+      ('aaaab', 'a4b1'), # 41
+      ('aaaabb', 'a4b2'), # 42
+      ('aaaabbb', 'a4b3'), # 43
+      ('aaaabbbb', 'a4b4'), # 44
+
+      ('abc', 'abc'), # 111
+      ('abcc', 'abcc'), # 112
+      ('abccc', 'abccc'), # 113
+      ('abbc', 'abbc'), # 121
+      ('abbcc', 'abbcc'), # 122
+      ('abbccc', 'abbccc'), # 123
+      ('abbbc', 'abbbc'), # 131
+      ('abbbcc', 'abbbcc'), # 132
+      ('abbbccc', 'a1b3c3'), # 133
+      ('aabc', 'aabc'), # 211
+      ('aabcc', 'aabcc'), # 212
+      ('aabccc', 'aabccc'), # 213
+      ('aabbc', 'aabbc'), # 221
+      ('aabbcc', 'aabbcc'), # 222
+      ('aabbccc', 'a2b2c3'), # 223
+      ('aabbbc', 'aabbbc'), # 231
+      ('aabbbcc', 'a2b3c2'), # 232
+      ('aabbbccc', 'a2b3c3'), # 233
+      ('aaabc', 'aaabc'), # 311
+      ('aaabcc', 'aaabcc'), # 312
+      ('aaabccc', 'a3b1c3'), # 313
+      ('aaabbc', 'aaabbc'), # 321
+      ('aaabbcc', 'a3b2c2'), # 322
+      ('aaabbccc', 'a3b2c3'), # 323
+      ('aaabbbc', 'a3b3c1'), # 331
+      ('aaabbbcc', 'a3b3c2'), # 332
+      ('aaabbbccc', 'a3b3c3'), # 333
+
+      ('aabcccccaaa', 'a2b1c5a3'),
+    ]
+
+  def func_provider(self):
+    return [
+      str_comp,
+    ]
+
+  def func_eval(self, func, args):
+    return func(args)
+
+if __name__ == '__main__':
+  unittest.main()