Add Soulution.go for 0018.4Sum

Author: Yeqi Tao

solution/0018.4Sum/Solution.go

@@ -0,0 +1,78 @@
+import "strconv"
+
+type Entry struct {
+	a1, a2, a3, a4 int
+}
+
+func(e *Entry) String() string {
+	return strconv.FormatInt(int64(e.a1), 10) +
+		"," + strconv.FormatInt(int64(e.a2), 10) +
+		"," + strconv.FormatInt(int64(e.a3), 10) +
+		"," + strconv.FormatInt(int64(e.a4), 10)
+}
+
+func fourSum(nums []int, target int) [][]int {
+	flag := make(map[string]bool)
+	sort(nums)
+	result := make([][]int, 0)
+	begin := 0
+	lenNums := len(nums) - 1
+	for begin + 2 < lenNums {
+		left := begin + 1
+		right := lenNums
+		lt := target - nums[begin]
+		for left + 1 < right {
+			i := left + 1
+			j := right
+			subTarget := lt - nums[left]
+			for i < j {
+				if nums[i] + nums[j] > subTarget {
+					j--
+				} else if nums[i] + nums[j] < subTarget {
+					i++
+				} else {
+					entry := &Entry{
+						a1:nums[begin],
+						a2:nums[left],
+						a3:nums[i],
+						a4:nums[j],
+					}
+					if !flag[entry.String()] {
+						r := []int{nums[begin], nums[left], nums[i], nums[j]}
+						result = append(result, r)
+						flag[entry.String()] = true
+					}
+					i++
+					j--
+				}
+			}
+			left++
+		}
+		begin++
+	}
+	return result
+}
+
+// quick sort
+func sort(array []int) {
+	if len(array) == 0 {
+		return
+	}
+	left := 0
+	right := len(array) - 1
+	obj := array[left]
+	for left < right {
+		for left < right && array[right] >= obj {
+			right--
+		}
+		array[left] = array[right]
+
+		for left < right && array[left] <= obj {
+			left++
+		}
+		array[right] = array[left]
+	}
+	array[left] = obj
+	sort(array[:left])
+	sort(array[right+1:])
+}