Find the duplicate number

Author: volodimyr

287.find_the_duplicate_number/find.go

@@ -0,0 +1,50 @@
+// 287. Find the duplicate number
+// Topics: 'Array', 'Two Pointers', 'Binary Search', 'Bit Manipulation'
+// Level: 'Medium'
+
+// Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.
+
+// There is only one repeated number in nums, return this repeated number.
+
+// You must solve the problem without modifying the array nums and using only constant extra space.
+
+// Example 1:
+
+// Input: nums = [1,3,4,2,2]
+// Output: 2
+
+// Example 2:
+
+// Input: nums = [3,1,3,4,2]
+// Output: 3
+
+// Example 3:
+
+// Input: nums = [3,3,3,3,3]
+// Output: 3
+
+// Constraints:
+
+//     1 <= n <= 105
+//     nums.length == n + 1
+//     1 <= nums[i] <= n
+//     All the integers in nums appear only once except for precisely one integer which appears two or more times.
+
+package findtheduplicatenumber
+
+func findDuplicate(nums []int) int {
+	slow, fast := nums[0], nums[0]
+	for {
+		slow = nums[slow]
+		fast = nums[nums[fast]]
+		if fast == slow {
+			break
+		}
+	}
+	slow2 := nums[0]
+	for slow2 != slow {
+		slow = nums[slow]
+		slow2 = nums[slow2]
+	}
+	return slow
+}

287.find_the_duplicate_number/find_test.go

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+package findtheduplicatenumber
+
+import "testing"
+
+func TestFindDuplicate_Example1(t *testing.T) {
+	nums := []int{1, 3, 4, 2, 2}
+	result := findDuplicate(nums)
+
+	if result != 2 {
+		t.Errorf("Expected 2, got %d", result)
+	}
+}
+
+func TestFindDuplicate_Example2(t *testing.T) {
+	nums := []int{3, 1, 3, 4, 2}
+	result := findDuplicate(nums)
+
+	if result != 3 {
+		t.Errorf("Expected 3, got %d", result)
+	}
+}
+
+func TestFindDuplicate_Example3(t *testing.T) {
+	nums := []int{3, 3, 3, 3, 3}
+	result := findDuplicate(nums)
+
+	if result != 3 {
+		t.Errorf("Expected 3, got %d", result)
+	}
+}
+
+func TestFindDuplicate_TwoElements(t *testing.T) {
+	nums := []int{1, 1}
+	result := findDuplicate(nums)
+
+	if result != 1 {
+		t.Errorf("Expected 1, got %d", result)
+	}
+}
+
+func TestFindDuplicate_Complex(t *testing.T) {
+	nums := []int{2, 5, 9, 6, 9, 3, 8, 9, 7, 1}
+	result := findDuplicate(nums)
+
+	if result != 9 {
+		t.Errorf("Expected 9, got %d", result)
+	}
+}
+
+func TestFindDuplicate_DuplicateAtEnd(t *testing.T) {
+	nums := []int{1, 2, 3, 4, 4}
+	result := findDuplicate(nums)
+
+	if result != 4 {
+		t.Errorf("Expected 4, got %d", result)
+	}
+}
+
+func TestFindDuplicate_DuplicateInMiddle(t *testing.T) {
+	nums := []int{1, 2, 5, 3, 5, 4}
+	result := findDuplicate(nums)
+
+	if result != 5 {
+		t.Errorf("Expected 5, got %d", result)
+	}
+}
+
+func TestFindDuplicate_ThreeElements(t *testing.T) {
+	nums := []int{2, 1, 2}
+	result := findDuplicate(nums)
+
+	if result != 2 {
+		t.Errorf("Expected 2, got %d", result)
+	}
+}
+
+func TestFindDuplicate_FourElements(t *testing.T) {
+	nums := []int{4, 3, 1, 4, 2}
+	result := findDuplicate(nums)
+
+	if result != 4 {
+		t.Errorf("Expected 4, got %d", result)
+	}
+}
+
+func TestFindDuplicate_LargerArray(t *testing.T) {
+	nums := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 5}
+	result := findDuplicate(nums)
+
+	if result != 5 {
+		t.Errorf("Expected 5, got %d", result)
+	}
+}
+
+func TestFindDuplicate_DuplicateOne(t *testing.T) {
+	nums := []int{1, 1, 2, 3, 4}
+	result := findDuplicate(nums)
+
+	if result != 1 {
+		t.Errorf("Expected 1, got %d", result)
+	}
+}
+
+func TestFindDuplicate_MultipleDuplicates(t *testing.T) {
+	nums := []int{2, 5, 9, 6, 9, 3, 8, 9, 7, 1, 4}
+	result := findDuplicate(nums)
+
+	if result != 9 {
+		t.Errorf("Expected 9, got %d", result)
+	}
+}
+
+func TestFindDuplicate_AdjacentDuplicates(t *testing.T) {
+	nums := []int{1, 2, 3, 3, 4, 5}
+	result := findDuplicate(nums)
+
+	if result != 3 {
+		t.Errorf("Expected 3, got %d", result)
+	}
+}
+
+func TestFindDuplicate_NonAdjacentDuplicates(t *testing.T) {
+	nums := []int{5, 1, 2, 3, 4, 5}
+	result := findDuplicate(nums)
+
+	if result != 5 {
+		t.Errorf("Expected 5, got %d", result)
+	}
+}
+
+func TestFindDuplicate_LargeN(t *testing.T) {
+	nums := make([]int, 101)
+	for i := 1; i <= 100; i++ {
+		nums[i-1] = i
+	}
+	nums[100] = 50
+
+	result := findDuplicate(nums)
+
+	if result != 50 {
+		t.Errorf("Expected 50, got %d", result)
+	}
+}
+
+func TestFindDuplicate_MaxValue(t *testing.T) {
+	nums := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10}
+	result := findDuplicate(nums)
+
+	if result != 10 {
+		t.Errorf("Expected 10, got %d", result)
+	}
+}
+
+func TestFindDuplicate_SequentialWithGap(t *testing.T) {
+	nums := []int{2, 5, 1, 3, 4, 6, 7, 3}
+	result := findDuplicate(nums)
+
+	if result != 3 {
+		t.Errorf("Expected 3, got %d", result)
+	}
+}
+
+func TestFindDuplicate_ReverseOrder(t *testing.T) {
+	nums := []int{5, 4, 3, 2, 1, 3}
+	result := findDuplicate(nums)
+
+	if result != 3 {
+		t.Errorf("Expected 3, got %d", result)
+	}
+}