Algocode: add two_sums solution

algocode/hash_tables/two_sum.py

@@ -0,0 +1,120 @@
+"""
+Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
+
+You may assume that each input would have exactly one solution, and you may not use the same element twice.
+
+You can return the answer in any order.
+
+Example 1:
+
+Input: nums = [2,7,11,15], target = 9
+Output: [0,1]
+Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
+Example 2:
+
+Input: nums = [3,2,4], target = 6
+Output: [1,2]
+Example 3:
+
+Input: nums = [3,3], target = 6
+Output: [0,1]
+
+Constraints:
+
+2 <= nums.length <= 104
+-109 <= nums[i] <= 109
+-109 <= target <= 109
+Only one valid answer exists.
+"""
+
+
+"""
+Допустим у нас будет хэшмапа, где будет лежать следующая пара ключ-значение:
+
+    {
+        <сколько_не_хватает_до_цели> : <list_position>
+    }
+
+Пробуем пройтись по очереди на первом примере
+0. delta = {}
+1. nums[0] = 2
+
+delta = {
+    7:0
+}
+
+2. nums[1] = 7
+2.1 Проверяем, есть ли в delta ключ `0`?
+2.2 Да - получается наш ответ : [0,1]
+
+---
+
+Example 2
+Input: nums = [3,2,4], target = 6
+
+0. delta = {}
+1. nums[0] = 3
+sub = target - 3 = 3
+
+delta = {
+    3:0
+}
+
+2.  nums[1] = 2
+2.0 index = 1
+2.1 Есть ли в delta ключ 2? -> нет, следовательно:
+2.2 sub = target - 2 = 4
+
+delta = {
+    3:0
+    4:1
+}
+
+3.  nums[2] = 4
+3.0 index = 2
+3.1 Есть ли в delta ключ 4? -> Есть
+3.2 Возвращаем [delta[4], index]
+
+
+"""
+
+class Solution:
+    def twoSum(self, nums, target: int):
+        if len(nums) == 2:
+            return [0,1]
+        delta = dict()
+        for index, element in enumerate(nums):
+            if index == 0:
+                delta[target - element] = index
+                continue
+            res = delta.get(element)
+            if isinstance(res, int):
+                return [index, res]
+            sub = target - element
+            delta[sub] = index
+        raise ValueError("Cannot find valid answer")
+
+s = Solution()
+nums = [2,7,11,15]
+target = 9
+# Output: [0,1]
+"""
+1
+delta = {
+    7:0
+}
+
+2
+
+"""
+assert s.twoSum(nums, target) in [[0,1], [1,0]], f"result = {s.twoSum(nums,target)}"
+
+nums = [3,2,4]
+target = 6
+# Output: [1,2]
+assert s.twoSum(nums, target) in [[1,2], [2,1]]
+
+nums = [3,3]
+target = 6
+# Output: [0,1]
+assert s.twoSum(nums, target) in [[0,1], [1,0]]