feat(arrays, subarrays): count subarrays with fixed bounds

Author: BrianLusina

datastructures/arrays/subarrays_with_fixed_bounds/README.md

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+# Count Subarrays with Fixed Bounds
+
+Given an integer array, nums, and two integers minK and maxK, return the number of fixed-bound subarrays.
+
+A subarray in nums is called a fixed-bound subarray if it satisfies the following conditions:
+
+1. The smallest value in the subarray equals `minK`.
+2. The largest value in the subarray equals `maxK`.
+
+> Note: A subarray is a contiguous sequence of elements within an array.
+
+Constraints:
+
+- 2 ≤ nums.length ≤ 10^3
+- 1 ≤ nums[i], minK, maxK ≤10^3
+
+## Examples
+
+![Example One](./images/subarrays_with_fixed_bounds_example_one.png)
+![Example Two](./images/subarrays_with_fixed_bounds_example_two.png)
+![Example Three](./images/subarrays_with_fixed_bounds_example_three.png)
+![Example Four](./images/subarrays_with_fixed_bounds_example_four.png)

datastructures/arrays/subarrays_with_fixed_bounds/__init__.py

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+from typing import List
+
+
+def count_subarrays(nums: List[int], min_k: int, max_k: int) -> int:
+    """
+    Counts the number of subarrays in the provided array which satisfies the following conditions:
+    1. The smallest value in the subarray equals min_k.
+    2. The largest value in the subarray equals max_k.
+
+    Args:
+        nums (List[int]): The array of integers.
+        min_k (int): The minimum value in the subarray.
+        max_k (int): The maximum value in the subarray.
+
+    Returns:
+        int: The number of subarrays that satisfies the conditions.
+    """
+    last_min, last_max, last_invalid = -1, -1, -1
+    count = 0
+
+    for i, num in enumerate(nums):
+        if num == min_k:
+            last_min = i
+        if num == max_k:
+            last_max = i
+        if num < min_k or num > max_k:
+            last_invalid = i
+
+        count += max(0, min(last_min, last_max) - last_invalid)
+
+    return count

datastructures/arrays/subarrays_with_fixed_bounds/images/subarrays_with_fixed_bounds_example_four.png

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+import unittest
+from . import count_subarrays
+
+
+class SubarraysWithFixedBoundsTestCase(unittest.TestCase):
+    def test_1(self):
+        nums = [2,1,4,3,2]
+        min_k = 2
+        max_k = 3
+        expected = 1
+        actual = count_subarrays(nums=nums, min_k=min_k, max_k=max_k)
+        self.assertEqual(expected, actual)
+
+    def test_2(self):
+        nums = [1,2,3,2,1]
+        min_k = 1
+        max_k = 3
+        expected = 5
+        actual = count_subarrays(nums=nums, min_k=min_k, max_k=max_k)
+        self.assertEqual(expected, actual)
+
+    def test_3(self):
+        nums = [4,4,4]
+        min_k = 4
+        max_k = 4
+        expected = 6
+        actual = count_subarrays(nums=nums, min_k=min_k, max_k=max_k)
+        self.assertEqual(expected, actual)
+
+    def test_4(self):
+        nums = [2,2,2]
+        min_k = 4
+        max_k = 4
+        expected = 0
+        actual = count_subarrays(nums=nums, min_k=min_k, max_k=max_k)
+        self.assertEqual(expected, actual)
+
+    def test_5(self):
+        nums = [1,3,5,2,7,5]
+        min_k = 1
+        max_k = 5
+        expected = 2
+        actual = count_subarrays(nums=nums, min_k=min_k, max_k=max_k)
+        self.assertEqual(expected, actual)
+
+    def test_6(self):
+        nums = [3,3,3]
+        min_k = 3
+        max_k = 3
+        expected = 6
+        actual = count_subarrays(nums=nums, min_k=min_k, max_k=max_k)
+        self.assertEqual(expected, actual)
+
+
+if __name__ == '__main__':
+    unittest.main()