adding Problem 18

Author: aQua

Algorithms/0018.4sum/4sum.go

@@ -1,2 +1,29 @@
 package Problem0018
 
+import (
+	"sort"
+)
+
+func fourSum(nums []int, target int) [][]int {
+	res := [][]int{}
+	sort.Ints(nums)
+
+	for i := 0; i < len(nums)-3; i++ {
+		for j := i + 1; j < len(nums)-2; j++ {
+			l, r := j+1, len(nums)-1
+			for l < r {
+
+				s := nums[i] + nums[j] + nums[l] + nums[r]
+				switch {
+				case s < target:
+					l++
+				case s > target:
+					r--
+				default:
+				}
+			}
+		}
+
+	}
+	return res
+}

Algorithms/0018.4sum/4sum_test.go

@@ -1,8 +1,8 @@
 package Problem0018
 
 import (
-	"testing"
 	"fmt"
+	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -15,13 +15,14 @@ type question struct {
 // para 是参数
 // one 代表第一个参数
 type para struct {
-	one string
+	one []int
+	two int
 }
 
 // ans 是答案
 // one 代表第一个答案
 type ans struct {
-	one string
+	one [][]int
 }
 
 func Test_Problem0018(t *testing.T) {
@@ -30,17 +31,21 @@ func Test_Problem0018(t *testing.T) {
 	qs := []question{
 
 		question{
-			para{""},
-			ans{""},
+			para{[]int{1, 0, -1, 0, -2, 2}, 0},
+			ans{[][]int{
+				[]int{-1, 0, 0, 1},
+				[]int{-2, -1, 1, 2},
+				[]int{-2, 0, 0, 2},
+			}},
 		},
-	
+
 		// 如需多个测试，可以复制上方元素。
 	}
 
 	for _, q := range qs {
 		a, p := q.ans, q.para
 		fmt.Printf("~~%v~~\n", p)
 
-		ast.Equal(a.one, (p.one), "输入:%v", p)
+		ast.Equal(a.one, fourSum(p.one, p.two), "输入:%v", p)
 	}
 }

Algorithms/0018.4sum/README.md

@@ -1,8 +1,19 @@
 # [18. 4Sum](https://leetcode.com/problems/4sum/)
 
 ## 题目
+Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
 
+Note: The solution set must not contain duplicate quadruplets.
+```
+For example, given array S = [1, 0, -1, 0, -2, 2], and target = 0.
 
+A solution set is:
+[
+  [-1,  0, 0, 1],
+  [-2, -1, 1, 2],
+  [-2,  0, 0, 2]
+]
+```
 ## 解题思路