add solution task #15 3Sum

Author: dmitryburov

Diff for: README.md

@@ -263,6 +263,7 @@
   <summary>Задачи с Leetcode</summary>
 
   - [X] [1. Two Sum](sprint_leetcode/1)
+  - [X] [15. 3Sum](sprint_leetcode/15)
   - [X] [19. Remove Nth Node From End of List](sprint_leetcode/19)
   - [X] [33. Search in Rotated Sorted Array](sprint_leetcode/33)
   - [X] [56. Merge Intervals](sprint_leetcode/56)

Diff for: sprint_leetcode/15/README.md

@@ -0,0 +1,3 @@
+# 15. 3Sum
+
+Подробнее о задаче: [Тыц](https://leetcode.com/problems/3sum/description/)

Diff for: sprint_leetcode/15/solution.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"sort"
+)
+
+func threeSum(nums []int) [][]int {
+	var res [][]int
+
+	sort.Ints(nums)
+
+	for i := 0; i < len(nums)-2; i++ {
+		if i == 0 || (i > 0 && nums[i] != nums[i-1]) {
+			low := i + 1
+			high := len(nums) - 1
+			sum := 0 - nums[i]
+
+			for low < high {
+				if (nums[low] + nums[high]) == sum {
+					res = append(res, []int{nums[i], nums[low], nums[high]})
+					for low < high && nums[low] == nums[low+1] {
+						low++
+					}
+					for low < high && nums[high] == nums[high-1] {
+						high--
+					}
+					low++
+					high--
+				} else if nums[low]+nums[high] > sum {
+					high--
+				} else {
+					low++
+				}
+			}
+		}
+	}
+
+	return res
+}

Diff for: sprint_leetcode/15/solution_test.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+type TestItemInput struct {
+	nums []int
+}
+type TestItem struct {
+	input  TestItemInput
+	output [][]int
+}
+
+func TestTask(t *testing.T) {
+	for i, v := range generateTasks() {
+		t.Run(fmt.Sprintf("Test %d", i+1), func(t *testing.T) {
+			res := threeSum(v.input.nums)
+			if !reflect.DeepEqual(res, v.output) {
+				t.Errorf("Wrong test.\nOutput: \n%v \nExpected: \n%v", res, v.output)
+			}
+		})
+	}
+}
+
+func generateTasks() []TestItem {
+	return []TestItem{
+		{
+			input:  TestItemInput{nums: []int{-1, 0, 1, 2, -1, -4}},
+			output: [][]int{{-1, -1, 2}, {-1, 0, 1}},
+		},
+		{
+			input:  TestItemInput{nums: []int{0, 1, 1}},
+			output: nil,
+		},
+		{
+			input:  TestItemInput{nums: []int{0, 0, 0}},
+			output: [][]int{{0, 0, 0}},
+		},
+	}
+}