add new solutions

solutions/0/q15/solution.go

@@ -0,0 +1,65 @@
+package q15
+
+import "slices"
+
+func sortAndDedup3(nums []int) []int {
+	slices.Sort(nums)
+	head, dup := 0, 0
+	for i := 1; i < len(nums); i++ {
+		if nums[i] == nums[head] {
+			dup++
+		} else {
+			dup = 0
+		}
+		if dup < 3 {
+			head++
+			nums[head] = nums[i]
+		}
+	}
+	return nums[:head+1]
+}
+
+func threeSum(nums []int) [][]int {
+	nums = sortAndDedup3(nums)
+	ret := [][]int{}
+
+	appendResult := func(a, b, c int) {
+		triplet := []int{a, b, c}
+		if len(ret) > 0 && slices.Equal(triplet, ret[len(ret)-1]) {
+			return
+		}
+		ret = append(ret, triplet)
+	}
+
+	for i := 0; i < len(nums)-2; i++ {
+		if nums[i] > 0 {
+			break
+		}
+		wants := -nums[i]
+		l, r := i+1, len(nums)-1
+		for l < r {
+			for l < r && nums[l]+nums[r] > wants {
+				r--
+			}
+			if l < r && nums[l]+nums[r] == wants {
+				appendResult(nums[i], nums[l], nums[r])
+				r--
+			}
+			for l < r && nums[l]+nums[r] < wants {
+				l++
+			}
+			if l < r && nums[l]+nums[r] == wants {
+				appendResult(nums[i], nums[l], nums[r])
+				l++
+			}
+		}
+
+		// skip same numbers
+		for ; i < len(nums)-2 && nums[i] == nums[i+1]; i++ {
+		}
+	}
+
+	return ret
+}
+
+var _ = threeSum

solutions/0/q20/solution.go

@@ -0,0 +1,32 @@
+package q20
+
+func isValid(s string) bool {
+	stack := make([]byte, 0, len(s)/2)
+
+	for i := range len(s) {
+		switch s[i] {
+		case '(', '[', '{':
+			stack = append(stack, s[i])
+		case ')':
+			if len(stack) == 0 || stack[len(stack)-1] != '(' {
+				return false
+			}
+			stack = stack[:len(stack)-1]
+
+		case ']':
+			if len(stack) == 0 || stack[len(stack)-1] != '[' {
+				return false
+			}
+			stack = stack[:len(stack)-1]
+
+		case '}':
+			if len(stack) == 0 || stack[len(stack)-1] != '{' {
+				return false
+			}
+			stack = stack[:len(stack)-1]
+		}
+	}
+	return len(stack) == 0
+}
+
+var _ = isValid