added Problem 15

Author: aQua

Algorithms/0015.3sum/3sum.go

@@ -1,47 +1,53 @@
 package Problem0015
 
-import (
-	"sort"
-)
+import "sort"
 
 func threeSum(nums []int) [][]int {
+	// 排序后，可以按规律查找
+	sort.Ints(nums)
 	res := [][]int{}
 
-	for i := 0; i < len(nums)-2; i++ {
-		for j := i + 1; j < len(nums)-1; j++ {
-			for k := j + 1; k < len(nums); k++ {
-				if nums[i]+nums[j]+nums[k] == 0 {
-					temp := []int{nums[i], nums[j], nums[k]}
-					if yes := contain(res, temp); !yes {
-						res = append(res, temp)
+	for i := range nums {
+		// 避免添加重复的结果
+		if i > 0 && nums[i] == nums[i-1] {
+			continue
+		}
 
-					}
-				}
+		l, r := i+1, len(nums)-1
+
+		for l < r {
+			s := nums[i] + nums[l] + nums[r]
+			switch {
+			case s < 0:
+				// 较小的 l 需要变大
+				l++
+			case s > 0:
+				// 较大的 r 需要变小
+				r--
+			default:
+				res = append(res, []int{nums[i], nums[l], nums[r]})
+				// 为避免重复添加，l 和 r 都需要移动到不同的元素上。
+				l, r = next(nums, l, r)
 			}
 		}
 	}
 
 	return res
 }
 
-func contain(numss [][]int, nums []int) bool {
-	sort.Ints(nums)
-
-	for _, ns := range numss {
-		sort.Ints(ns)
-		if equal(ns, nums) {
-			return true
+func next(nums []int, l, r int) (int, int) {
+	for l < r {
+		switch {
+		case nums[l] == nums[l+1]:
+			l++
+		case nums[r] == nums[r-1]:
+			r--
+		default:
+			l++
+			r--
+			return l, r
 		}
 	}
 
-	return false
-}
-
-func equal(a, b []int) bool {
-	for i, v := range a {
-		if v != b[i] {
-			return false
-		}
-	}
-	return true
+	return l, r
 }

Algorithms/0015.3sum/3sum_test.go

@@ -1,6 +1,7 @@
 package Problem0015
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -29,10 +30,36 @@ func Test_Problem0015(t *testing.T) {
 	qs := []question{
 
 		question{
-			para{[]int{-1, 0, 1, 2, -1, -4}},
+			para{[]int{1, -1, -1, 0}},
 			ans{[][]int{
 				[]int{-1, 0, 1},
+			}},
+		},
+
+		question{
+			para{[]int{-1, 0, 1, 2, 2, 2, 2, -1, -4}},
+			ans{[][]int{
+				[]int{-4, 2, 2},
 				[]int{-1, -1, 2},
+				[]int{-1, 0, 1},
+			}},
+		},
+		question{
+			para{[]int{0, 0, 0, 0, 0}},
+			ans{[][]int{
+				[]int{0, 0, 0},
+			}},
+		},
+		question{
+			para{[]int{1, 1, -2}},
+			ans{[][]int{
+				[]int{-2, 1, 1},
+			}},
+		},
+		question{
+			para{[]int{0, 0, 0}},
+			ans{[][]int{
+				[]int{0, 0, 0},
 			}},
 		},
 
@@ -43,5 +70,6 @@ func Test_Problem0015(t *testing.T) {
 		a, p := q.ans, q.para
 
 		ast.Equal(a.one, threeSum(p.one), "输入:%v", p)
+		fmt.Println("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~")
 	}
 }

Algorithms/0015.3sum/README.md

@@ -1,11 +1,19 @@
 # [15. 3Sum](https://leetcode.com/problems/3sum/)
 
 ## 题目
+Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
 
+Note: The solution set must not contain duplicate triplets.
+```
+For example, given array S = [-1, 0, 1, 2, -1, -4],
 
+A solution set is:
+[
+  [-1, 0, 1],
+  [-1, -1, 2]
+]
+```
 ## 解题思路
+穷举法无法通过时间限制
 
-
-## 总结
-
-
+详见代码