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 +1,30 @@
+func isAlnum(r rune) bool {
+	return unicode.IsLetter(r) || unicode.IsDigit(r)
+}
+
+func isPalindromeValid(input string) bool {
+	s := []rune(input)
+
+	left, right := 0, len(s)-1
+
+	for left < right {
+		// Skip non-alphanumeric characters from the left.
+		for left < right && !isAlnum(s[left]) {
+			left++
+		}
+		// Skip non-alphanumeric characters from the right.
+		for left < right && !isAlnum(s[right]) {
+			right--
+		}
+		// If the characters at the left and right pointers don't
+		// match, the string is not a palindrome.
+		if s[left] != s[right] {
+			return false
+		}
+
+		left++
+		right--
+	}
+
+	return true
+}

go/Two Pointers/largest_container.go

@@ -0,0 +1,24 @@
+func largestContainer(heights []int) int {
+	maxWater := 0
+	left, right := 0, len(heights)-1
+
+	for left < right {
+		// Calculate the water contained between the current pair of
+		// lines.
+		water := min(heights[left], heights[right]) * (right - left)
+		maxWater = max(maxWater, water)
+		// Move the pointers inward, always moving the pointer at the
+		// shorter line. If both lines have the same height, move both
+		// pointers inward.
+		if heights[left] < heights[right] {
+			left++
+		} else if heights[left] > heights[right] {
+			right--
+		} else {
+			left++
+			right--
+		}
+	}
+
+	return maxWater
+}

go/Two Pointers/next_lexicographical_sequence.go

@@ -0,0 +1,35 @@
+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)
+	// Locate the pivot, which is the first character from the right that breaks
+	// non-increasing order. Start searching from the second-to-last position.
+	pivot := len(letters) - 2
+	for pivot >= 0 && letters[pivot] >= letters[pivot+1] {
+		pivot--
+	}
+	// If pivot is not found, the string is already in its largest permutation. In
+	// this case, reverse the string to obtain the smallest permutation.
+	if pivot == -1 {
+		reverse(letters, 0)
+		return string(letters)
+	}
+	// Find the rightmost successor to the pivot.
+	rightmostSuccessor := len(letters) - 1
+	for letters[rightmostSuccessor] <= letters[pivot] {
+		rightmostSuccessor--
+	}
+	// Swap the rightmost successor with the pivot to increase the lexicographical
+	// order of the suffix.
+	letters[pivot], letters[rightmostSuccessor] = letters[rightmostSuccessor], letters[pivot]
+	// Reverse the suffix after the pivot to minimize its permutation.
+	reverse(letters, pivot+1)
+	return string(letters)
+}

go/Two Pointers/pair_sum_sorted.go

@@ -0,0 +1,19 @@
+func pairSumSorted(nums []int, target int) []int {
+	left, right := 0, len(nums)-1
+	for left < right {
+		sum := nums[left] + nums[right]
+		// If the sum is smaller, increment the left pointer, aiming
+		// to increase the sum toward the target value.
+		if sum < target {
+			left++
+		} else if sum > target {
+			// If the sum is larger, decrement the right pointer, aiming
+			// to decrease the sum toward the target value.
+			right--
+		} else {
+			// If the target pair is found, return its indexes.
+			return []int{left, right}
+		}
+	}
+	return []int{}
+}

go/Two Pointers/shift_zeros_to_the_end.go

@@ -0,0 +1,14 @@
+func shiftZerosToTheEnd(nums []int) {
+	// The 'left' pointer is used to position non-zero elements.
+	left := 0
+	// Iterate through the array using a 'right' pointer to locate non-zero
+	// elements.
+	for right := 0; right < len(nums); right++ {
+		if nums[right] != 0 {
+			nums[left], nums[right] = nums[right], nums[left]
+			// Increment 'left' since it now points to a position already occupied
+			// by a non-zero element.
+			left++
+		}
+	}
+}

go/Two Pointers/triplet_sum.go

@@ -0,0 +1,50 @@
+func tripletSum(nums []int) [][]int {
+	triplets := [][]int{}
+	sort.Ints(nums)
+
+	for i := 0; i < len(nums); i++ {
+		// Optimization: triplets consisting of only positive numbers
+		// will never sum to 0.
+
+		if nums[i] > 0 {
+			break
+		}
+
+		// To avoid duplicate triplets, skip 'a' if it's the same as
+		// the previous number.
+		if i > 0 && nums[i] == nums[i-1] {
+			continue
+		}
+
+		// Find all pairs that sum to a target of '-a' (-nums[i]).
+		pairs := pairSumSortedAllPairs(nums, i+1, -nums[i])
+		for _, pair := range pairs {
+			triplets = append(triplets, []int{nums[i], pair[0], pair[1]})
+		}
+	}
+
+	return triplets
+}
+
+func pairSumSortedAllPairs(nums []int, start int, target int) [][]int {
+	pairs := [][]int{}
+	left, right := start, len(nums)-1
+	for left < right {
+		sum := nums[left] + nums[right]
+		if sum == target {
+			pairs = append(pairs, []int{nums[left], nums[right]})
+			left++
+			// To avoid duplicate '[b, c]' pairs, skip 'b' if it's the
+			// same as the previous number.
+			for left < right && nums[left] == nums[left-1] {
+				left++
+			}
+		} else if sum < target {
+			left++
+		} else {
+			right--
+		}
+	}
+
+	return pairs
+}