15. 3Sum

.travis.yml

@@ -1,7 +1,7 @@
 language: go
 
 go:
-  - "1.11.x"
+  - "1.12.x"
 
 go_import_path: leetcode
 

README.md

@@ -13,6 +13,7 @@ continually updating 😃.
 * [1. Two Sum](src/0001_two_sum/twosum.go)   *`lookup table;`*  *`hash table`*
 * [4. Median of Two Sorted Arrays](src/0004_median_of_two_sorted_arrays/motsa.go)   *`binary search;`*  *`divide and conquer`*
 * [11. Container With Most Water](src/0011_container_with_most_water/container_with_most_water.go)   *`double index;`*  *`array`*
+* [15. 3Sum](src/0015_3Sum/3sum.go)   *`double index;`*  *`array`*
 * [26. Remove Duplicates from Sorted Array](src/0026_remove_duplicates_from_sorted_array/rdfsa.go)   *`double index;`*  *`array`*
 * [27. Remove Element](src/0027_remove_element/remove_element.go)   *`double index;`*  *`array`*
 * [48. Rotate Image](src/0048_rotate_image/rotate_image.go)

src/0015_3Sum/3sum.go

@@ -0,0 +1,44 @@
+/*
+15. 3Sum
+https://leetcode.com/problems/3sum/
+*/
+// time: 2019-03-01
+
+package threesum
+
+import "sort"
+
+// time complexity: O(n^2)
+func threeSum(nums []int) [][]int {
+	sort.Ints(nums)
+	var res [][]int
+	for i := 0; i < len(nums)-2; i++ {
+		if nums[i] > 0 {
+			break
+		}
+		if i > 0 && nums[i] == nums[i-1] {
+			continue
+		}
+		for l, r := i+1, len(nums)-1; l < r; {
+			if l > i+1 && nums[l] == nums[l-1] {
+				l++
+				continue
+			}
+			if r < len(nums)-1 && nums[r] == nums[r+1] {
+				r--
+				continue
+			}
+			switch sum := nums[i] + nums[l] + nums[r]; {
+			case sum < 0:
+				l++
+			case sum > 0:
+				r--
+			default:
+				res = append(res, []int{nums[i], nums[l], nums[r]})
+				l++
+				r--
+			}
+		}
+	}
+	return res
+}

src/0015_3Sum/3sum_test.go

@@ -0,0 +1,23 @@
+package threesum
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestThreeSum(t *testing.T) {
+	testData := [][]int{
+		{-1, 0, 1, 2, -6, -4},
+		{-7, 3, -7, 3, 4, 5, 6, 6, 4},
+	}
+	expected := [][][]int{
+		{{-1, 0, 1}},
+		{{-7, 3, 4}},
+	}
+
+	for index, nums := range testData {
+		if res := threeSum(nums); !reflect.DeepEqual(res, expected[index]) {
+			t.Errorf("expected %v, got %v", expected[index], res)
+		}
+	}
+}

src/README.md

@@ -11,6 +11,7 @@
 |0011|[11. Container With Most Water](0011_container_with_most_water/container_with_most_water.go)|Medium|*`array;`*  *`double index`*|
 |0013|[13. Roman to Integer](0013_roman_to_integer/roman_to_integer.go)|Easy|*`math`*|
 |0014|[14. Longest Common Prefix](0014_longest_common_prefix/lcp.go)|Easy||
+|0015|[15. 3Sum](0015_3Sum/3sum.go)|Medium||
 |0017|[Letter Combinations of a Phone Number](0017_letter_combination_of_a_phone_number/letter_combination_of_phone_number.go)|Medium|*`tree`*|
 |0019|[19. Remove Nth Node From End of List](0019_remove_nth_node_from_end_of_list/remove_nth_node_from_end_of_list.go)|Medium|*`linked list`*|
 |0020|[Valid Parentheses](0020_valid_parentheses/valid_parentheses.go)|Easy|*`string;`* *`stack`*|