Create longest_subarray_with_given_sum.py

data_structures/arrays/longest_subarray_with_given_sum.py

@@ -0,0 +1,59 @@
+"""
+Author  : Akash Singh
+Date    : October 19, 2024
+
+This module finds the longest subarray with a given sum.
+The algorithm uses a hash map to track cumulative sums and efficiently find subarrays.
+"""
+
+
+class LongestSubarrayWithGivenSum:
+    def __init__(self, array: list[int]) -> None:
+        self.array = array
+
+    def find_longest_subarray(self, target_sum: int) -> int:
+        """
+        This function returns the length of the longest subarray
+        that adds up to the target sum.
+
+        Runtime: O(n)
+        Space: O(n)
+
+        >>> LongestSubarrayWithGivenSum([1, -1, 5, -2, 3]).find_longest_subarray(3)
+        4
+        >>> LongestSubarrayWithGivenSum([-2, -1, 2, 1]).find_longest_subarray(1)
+        2
+        >>> LongestSubarrayWithGivenSum([3, 1, 0, 1, 8, -2, 3]).find_longest_subarray(8)
+        5
+        >>> LongestSubarrayWithGivenSum([1, 2, 3]).find_longest_subarray(6)
+        3
+        >>> LongestSubarrayWithGivenSum([5, 1, -1, 5, -1, -2]).find_longest_subarray(4)
+        3
+        >>> LongestSubarrayWithGivenSum([2, 4, 6, 8]).find_longest_subarray(7)
+        0
+        """
+        prefix_sum_map: dict[int, int] = {}
+        longest_length = 0
+        current_sum = 0
+
+        for i, num in enumerate(self.array):
+            current_sum += num
+
+            if current_sum == target_sum:
+                longest_length = i + 1  # If sum equals target from index 0
+
+            if current_sum - target_sum in prefix_sum_map:
+                longest_length = max(
+                    longest_length, i - prefix_sum_map[current_sum - target_sum]
+                )
+
+            if current_sum not in prefix_sum_map:
+                prefix_sum_map[current_sum] = i
+
+        return longest_length
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()