Create 0018-4Sum.go solution

Author: razer96

go/0018-4Sum.go

@@ -0,0 +1,45 @@
+func fourSum(nums []int, target int) [][]int {
+	if len(nums) < 4 {
+		return [][]int{}
+	}
+
+	sort.Ints(nums)
+
+	result := make([][]int, 0)
+
+	for i, ival := range nums {
+		if i != 0 && nums[i] == nums[i - 1] {
+			continue
+		}
+
+		for j := i + 1; j < len(nums) - 1; j++ {
+			if j != i+1 && nums[j] == nums[j-1] {
+				continue
+			}
+
+			jval := nums[j]
+
+			for l, r := j+1, len(nums) - 1; l < r; {
+				lval, rval := nums[l], nums[r]
+
+				sum := ival + jval + lval + rval
+				switch {
+				case sum < target:
+					l++
+				case sum > target:
+					r--
+				default:
+					result = append(result, []int{ival, jval, lval, rval})
+					for ; l < r && nums[l] == nums[l+1]; l++ {
+					}
+					for ; l < r && nums[r] == nums[r-1]; r-- {
+					}
+					l++
+					r--
+				}
+			}
+		}
+	}
+
+	return result
+}