adding Problem 18

Author: aQua

Algorithms/0018.4sum/4sum.go

@@ -9,21 +9,48 @@ func fourSum(nums []int, target int) [][]int {
 	sort.Ints(nums)
 
 	for i := 0; i < len(nums)-3; i++ {
+		// 避免添加重复的结果
+		if i > 1 && nums[i] == nums[i-2] {
+			continue
+		}
+
 		for j := i + 1; j < len(nums)-2; j++ {
+			// 避免添加重复的结果
+			if nums[j] == nums[j-1] {
+				continue
+			}
+
 			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:
+					res = append(res, []int{nums[i], nums[j], nums[l], nums[r]})
+					l, r = next(nums, l, r)
 				}
 			}
 		}
 
 	}
 	return res
 }
+
+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--
+			break
+		}
+	}
+	return l, r
+}

Algorithms/0018.4sum/4sum_test.go

@@ -33,9 +33,28 @@ func Test_Problem0018(t *testing.T) {
 		question{
 			para{[]int{1, 0, -1, 0, -2, 2}, 0},
 			ans{[][]int{
+				[]int{-2, -1, 1, 2},
+				[]int{-2, 0, 0, 2},
 				[]int{-1, 0, 0, 1},
+			}},
+		},
+		question{
+			para{[]int{0, 0, 0, 0}, 0},
+			ans{[][]int{
+				[]int{0, 0, 0, 0},
+			}},
+		},
+		question{
+			para{[]int{-1, -1, -2, -2, 1, 1, 2, 2, 0, 0, 0, 0}, 0},
+			ans{[][]int{
+				[]int{-2, -2, 2, 2},
 				[]int{-2, -1, 1, 2},
 				[]int{-2, 0, 0, 2},
+				[]int{-2, 0, 1, 1},
+				[]int{-1, -1, 0, 2},
+				[]int{-1, -1, 1, 1},
+				[]int{-1, 0, 0, 1},
+				[]int{0, 0, 0, 0},
 			}},
 		},