Added Golang solutions of 'Two Pointers' tasks

Signed-off-by: Slava Lysunkin <lysunkin@gmail.com>

Author: lysunkin

go/Two Pointers/is_palindrome_valid.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+)
+
+func isAlnum(r rune) bool {
+	return unicode.IsLetter(r) || unicode.IsDigit(r)
+}
+
+func isPalindromeValid(input string) bool {
+	s := []rune(strings.ToLower(input))
+	left, right := 0, len(s)-1
+
+	for left < right {
+		for !isAlnum(s[left]) && left < right {
+			left++
+		}
+		for !isAlnum(s[right]) && left < right {
+			right--
+		}
+
+		if s[left] != s[right] {
+			return false
+		}
+
+		left++
+		right--
+	}
+
+	return true
+}
+
+func main() {
+	fmt.Println(isPalindromeValid("A dog! A panic in a pagoda.")) // -> true
+	fmt.Println(isPalindromeValid("abc123"))                      // -> false
+}

go/Two Pointers/largest_container.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"fmt"
+)
+
+func largestContainer(heights []int) int {
+	left, right := 0, len(heights)-1
+	maxVol := 0
+
+	for left < right {
+		width := right - left
+		height := heights[left]
+		if heights[right] < height {
+			height = heights[right]
+		}
+		currentVol := width * height
+		if currentVol > maxVol {
+			maxVol = currentVol
+		}
+
+		if heights[left] < heights[right] {
+			left++
+		} else {
+			right--
+		}
+	}
+
+	return maxVol
+}
+
+func main() {
+	fmt.Println(largestContainer([]int{2, 7, 8, 3, 7, 6})) // -> 24
+}

go/Two Pointers/next_lexicographical_sequence.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"fmt"
+)
+
+func reverse(s []rune, start int) {
+	end := len(s) - 1
+	for start < end {
+		s[start], s[end] = s[end], s[start]
+		start++
+		end--
+	}
+}
+
+func nextLexicographicalSequence(s string) string {
+	letters := []rune(s)
+	n := len(letters)
+	pivot := n - 2
+
+	for pivot >= 0 && letters[pivot] >= letters[pivot+1] {
+		pivot--
+	}
+
+	if pivot == -1 {
+		reverse(letters, 0)
+		return string(letters)
+	}
+
+	successor := n - 1
+	for letters[successor] <= letters[pivot] {
+		successor--
+	}
+
+	letters[pivot], letters[successor] = letters[successor], letters[pivot]
+
+	reverse(letters, pivot+1)
+
+	return string(letters)
+}
+
+func main() {
+	fmt.Println(nextLexicographicalSequence("abcd")) // -> abdc
+	fmt.Println(nextLexicographicalSequence("dcba")) // -> abcd
+}

go/Two Pointers/pair_sum_sorted.go

@@ -0,0 +1,24 @@
+package main
+
+import "fmt"
+
+func pairSumSorted(nums []int, target int) []int {
+	left, right := 0, len(nums)-1
+	for left < right {
+		sum := nums[left] + nums[right]
+		if sum == target {
+			return []int{left, right}
+		}
+		if sum < target {
+			left++
+		} else {
+			right--
+		}
+	}
+	return []int{}
+}
+
+func main() {
+	fmt.Println(pairSumSorted([]int{-5, -2, 3, 4, 6}, 7)) // -> [2 3]
+	fmt.Println(pairSumSorted([]int{1, 1, 1}, 2))         // -> [0 2]
+}

go/Two Pointers/shift_zeros_to_the_end.go

@@ -0,0 +1,19 @@
+package main
+
+import "fmt"
+
+func shiftZerosToTheEnd(nums []int) {
+	left := 0
+	for right := 0; right < len(nums); right++ {
+		if nums[right] != 0 {
+			nums[left], nums[right] = nums[right], nums[left]
+			left++
+		}
+	}
+}
+
+func main() {
+	nums := []int{0, 1, 0, 3, 2}
+	shiftZerosToTheEnd(nums)
+	fmt.Println(nums) // -> [1 3 2 0 0]
+}

go/Two Pointers/triplet_sum.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+)
+
+func tripletSum(nums []int) [][]int {
+	result := [][]int{}
+
+	sort.Ints(nums)
+	n := len(nums)
+
+	for i := 0; i < n-2; i++ {
+		if i > 0 && nums[i] == nums[i-1] {
+			continue
+		}
+
+		left, right := i+1, n-1
+		for left < right {
+			sum := nums[i] + nums[left] + nums[right]
+			if sum == 0 {
+				result = append(result, []int{nums[i], nums[left], nums[right]})
+				left++
+				right--
+				for left < right && nums[left] == nums[left-1] {
+					left++
+				}
+				for left < right && nums[right] == nums[right+1] {
+					right--
+				}
+			} else if sum < 0 {
+				left++
+			} else {
+				right--
+			}
+		}
+	}
+
+	return result
+}
+
+func main() {
+	fmt.Println(tripletSum([]int{0, -1, 2, -3, 1})) // -> [[-3 1 2] [-1 0 1]]
+}