[Two Pointers][Two Sum II Input Array Is Sorted] - Implement solution for Leetcode 167

2_two_pointers/2_two_sum_II_input_array_is_sorted/solution.go

@@ -0,0 +1,64 @@
+package twosumiiinputarrayissorted
+
+// Time complexity: O(n^2)
+// Space complexity: O(1)
+func TwoSumBruteForce(nums []int, target int) []int {
+	for i := 0; i < len(nums); i++ {
+		for j := i + 1; j < len(nums); j++ {
+			if nums[i]+nums[j] == target {
+				return []int{i + 1, j + 1}
+			}
+		}
+	}
+	return nil
+}
+
+// Time complexity: O(n * log n)
+// Space complexity: O(1)
+func TwoSumBinarySearch(nums []int, target int) []int {
+	for i := range nums {
+		left, right := i+1, len(nums)-1
+		needed := target - nums[i]
+		for left <= right {
+			mid := left + (right-left)/2
+			if nums[mid] == needed {
+				return []int{i + 1, mid + 1}
+			} else if nums[mid] < needed {
+				left = mid + 1
+			} else {
+				right = mid - 1
+			}
+		}
+	}
+	return nil
+}
+
+// Time complexity: O(n)
+// Space complexity: O(n)
+func TwoSumHashMap(nums []int, target int) []int {
+	seen := make(map[int]int)
+	for i, num := range nums {
+		if j, ok := seen[target-num]; ok {
+			return []int{i + 1, j + 1}
+		}
+		seen[num] = i
+	}
+	return nil
+}
+
+// Time complexity: O(n)
+// Space complexity: O(1)
+func TwoSumTwoPointers(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 + 1, right + 1}
+		} else if sum < target {
+			left++
+		} else {
+			right--
+		}
+	}
+	return nil
+}

2_two_pointers/2_two_sum_II_input_array_is_sorted/solution_test.go

@@ -0,0 +1,46 @@
+package twosumiiinputarrayissorted
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestTwoSum(t *testing.T) {
+	cases := []struct {
+		name     string
+		fn       func([]int, int) []int
+		nums     []int
+		target   int
+		expected []int
+	}{
+		// TwoSumBruteForce
+		{"Brute Force - Basic", TwoSumBruteForce, []int{2, 7, 11, 15}, 9, []int{1, 2}},
+		{"Brute Force - Not Found", TwoSumBruteForce, []int{1, 2, 3}, 10, nil},
+		{"Brute Force - Single", TwoSumBruteForce, []int{5}, 5, nil},
+		{"Brute Force - Negative Numbers", TwoSumBruteForce, []int{-3, 0, 3, 4}, 0, []int{1, 3}},
+
+		// TwoSumBinarySearch
+		{"Binary Search - Basic", TwoSumBinarySearch, []int{2, 7, 11, 15}, 9, []int{1, 2}},
+		{"Binary Search - Not Found", TwoSumBinarySearch, []int{1, 2, 3}, 6, nil},
+		{"Binary Search - Negative Numbers", TwoSumBinarySearch, []int{-4, -1, 1, 2, 5}, 1, []int{1, 5}},
+
+		// TwoSumHashMap
+		{"Hash Map - Basic", TwoSumHashMap, []int{2, 7, 11, 15}, 9, []int{2, 1}},
+		{"Hash Map - Not Found", TwoSumHashMap, []int{1, 2, 3}, 0, nil},
+		{"Hash Map - Negative", TwoSumHashMap, []int{-3, 4, 3, 90}, 0, []int{3, 1}},
+
+		// TwoSumTwoPointers
+		{"Two Pointers - Basic", TwoSumTwoPointers, []int{2, 7, 11, 15}, 9, []int{1, 2}},
+		{"Two Pointers - Not Found", TwoSumTwoPointers, []int{1, 2, 3}, 7, nil},
+		{"Two Pointers - Edge", TwoSumTwoPointers, []int{-10, -3, 0, 1, 6}, -3, []int{2, 3}},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := c.fn(c.nums, c.target)
+			if !reflect.DeepEqual(got, c.expected) {
+				t.Errorf("%s failed: expected %v, got %v", c.name, c.expected, got)
+			}
+		})
+	}
+}