From 95db17ce0f436f4ced6949ef507dc2f07e696349 Mon Sep 17 00:00:00 2001 From: Shabab Karim Date: Mon, 26 Oct 2020 16:08:53 +0600 Subject: [PATCH] Added two pointer solution for two sum problem (#3468) --- other/two_pointer.py | 61 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) create mode 100644 other/two_pointer.py diff --git a/other/two_pointer.py b/other/two_pointer.py new file mode 100644 index 000000000..ff234cddc --- /dev/null +++ b/other/two_pointer.py @@ -0,0 +1,61 @@ +""" +Given a sorted array of integers, return indices of the two numbers such +that they add up to a specific target using the two pointers technique. + +You may assume that each input would have exactly one solution, and you +may not use the same element twice. + +This is an alternative solution of the two-sum problem, which uses a +map to solve the problem. Hence can not solve the issue if there is a +constraint not use the same index twice. [1] + +Example: +Given nums = [2, 7, 11, 15], target = 9, + +Because nums[0] + nums[1] = 2 + 7 = 9, +return [0, 1]. + +[1]: https://github.com/TheAlgorithms/Python/blob/master/other/two_sum.py +""" +from __future__ import annotations + + +def two_pointer(nums: list[int], target: int) -> list[int]: + """ + >>> two_pointer([2, 7, 11, 15], 9) + [0, 1] + >>> two_pointer([2, 7, 11, 15], 17) + [0, 3] + >>> two_pointer([2, 7, 11, 15], 18) + [1, 2] + >>> two_pointer([2, 7, 11, 15], 26) + [2, 3] + >>> two_pointer([1, 3, 3], 6) + [1, 2] + >>> two_pointer([2, 7, 11, 15], 8) + [] + >>> two_pointer([3 * i for i in range(10)], 19) + [] + >>> two_pointer([1, 2, 3], 6) + [] + """ + i = 0 + j = len(nums) - 1 + + while i < j: + + if nums[i] + nums[j] == target: + return [i, j] + elif nums[i] + nums[j] < target: + i = i + 1 + else: + j = j - 1 + + return [] + + +if __name__ == "__main__": + import doctest + + doctest.testmod() + print(f"{two_pointer([2, 7, 11, 15], 9) = }")