Cracking the coding interview initialisation

cracking-the-coding-interview/README.md

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+# Cracking the coding interview
+
+This sub dir has some extracted lessons from the CCTI book. It may not be complete.

cracking-the-coding-interview/vii/1-bottlenet.py

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+import unittest
+
+# Example: Given an array of distinct integer values,
+# count the number of pairs of integers that have difference k.
+# For example, given the array {1, 7, 5, 9, 2, 12, 3} and
+# the difference k = 2,there are four pairs with
+# difference 2: (1, 3), (3, 5), (5, 7), (7, 9).
+
+# the first approach is using brute force to iterate over the array nums
+# from i to n and internally doing it from i + 1 to n
+# until finding the last pair at (n, n).
+
+# the O(n) approach is to dump the complement into as key into the
+# hash table then iterate over the array again and try to find
+# each num as key in the table. If it can be found then
+# it has its pair.
+
+
+class Solution:
+    def finding_pairs_of_k(self, nums, k: int):
+        table = {}
+        count = 0
+
+        for num in nums:
+            table[num - k] = num
+
+        for num in nums:
+            if table.get(num, None):
+                count += 1
+
+        return count
+
+
+class Test(unittest.TestCase):
+    def setUp(self):
+        self.solution = Solution()
+
+    def test_first(self):
+        self.assertEqual(
+            self.solution.finding_pairs_of_k(nums=[1, 7, 5, 9, 2, 12, 3], k=2), 4
+        )
+
+    def test_second(self):
+        self.assertEqual(
+            self.solution.finding_pairs_of_k(nums=[1, 7, 5, 9, 2, 12, 3], k=10), 1
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()