problem: new problem solution - 287 . Find the Duplicate Number

README.md

@@ -72,6 +72,7 @@ My approach to solving LeetCode problems typically involves the following steps:
 | 1631 | [Path With Minimum Effort](https://leetcode.com/problems/path-with-minimum-effort/)                                                     | Algorithms | [TypeScript](./problems/algorithms/pathWithMinimumEffort/PathWithMinimumEffort.ts)                                         | Medium     |
 | 319  | [Bulb Switcher](https://leetcode.com/problems/bulb-switcher/)                                                                           | Algorithms | [TypeScript](./problems/algorithms/bulbSwitcher/BulbSwitcher.ts)                                                           | Medium     |
 | 1584 | [Min Cost to Connect All Points](https://leetcode.com/problems/min-cost-to-connect-all-points/)                                         | Algorithms | [TypeScript](./problems/algorithms/minCostToConnectAllPoints/MinCostToConnectAllPoints.ts)                                 | Medium     |
+| 287  | [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)                                                   | Algorithms | [TypeScript](./problems/algorithms/findTheDuplicateNumber/FindTheDuplicateNumber.ts)                                       | Medium     |
 | ...  | ...                                                                                                                                     | ...        | ...                                                                                                                        | ...        |
 
 In this table:

problems/algorithms/findTheDuplicateNumber/FindTheDuplicateNumber.test.ts

@@ -0,0 +1,59 @@
+// Source : https://leetcode.com/problems/find-the-duplicate-number/
+// Author : squxq
+// Date   : 2023-09-20
+
+import { findDuplicate } from "./FindTheDuplicateNumber"; // Replace with the actual path to your code file
+
+describe("findDuplicate", () => {
+  it("Test Case 1", () => {
+    const nums = [1, 3, 4, 2, 2];
+    expect(findDuplicate(nums)).toBe(2);
+  });
+
+  it("Test Case 2", () => {
+    const nums = [3, 1, 3, 4, 2];
+    expect(findDuplicate(nums)).toBe(3);
+  });
+
+  it("Test Case 3 (Minimum Input Size)", () => {
+    const nums = [1];
+    expect(findDuplicate(nums)).toBe(1);
+  });
+
+  it("Test Case 4 (Maximum Input Size)", () => {
+    const n = 100000;
+    const nums = Array.from({ length: n }, (_, i) => i + 1);
+    nums.push(99999); // Add a duplicate
+    expect(findDuplicate(nums)).toBe(99999);
+  });
+
+  it("Test Case 5 (Duplicate at the Beginning)", () => {
+    const nums = [2, 2, 3, 4, 5];
+    expect(findDuplicate(nums)).toBe(2);
+  });
+
+  it("Test Case 6 (Duplicate at the End)", () => {
+    const nums = [1, 2, 3, 4, 5, 5];
+    expect(findDuplicate(nums)).toBe(5);
+  });
+
+  it("Test Case 7 (Duplicate in the Middle)", () => {
+    const nums = [1, 2, 3, 3, 4, 5];
+    expect(findDuplicate(nums)).toBe(3);
+  });
+
+  it("Test Case 8 (Random Order)", () => {
+    const nums = [5, 2, 1, 3, 4, 4];
+    expect(findDuplicate(nums)).toBe(4);
+  });
+
+  it("Test Case 9 (Duplicates at Both Ends)", () => {
+    const nums = [1, 2, 1, 3, 4, 5, 5];
+    expect(findDuplicate(nums)).toBe(1);
+  });
+
+  it("Test Case 10 (All Elements Are the Same)", () => {
+    const nums = [7, 7, 7, 7, 7];
+    expect(findDuplicate(nums)).toBe(7);
+  });
+});

problems/algorithms/findTheDuplicateNumber/FindTheDuplicateNumber.ts

@@ -0,0 +1,78 @@
+// Source : https://leetcode.com/problems/find-the-duplicate-number/
+// Author : squxq
+// Date   : 2023-09-20
+
+/*****************************************************************************************************
+ *
+ * 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 uses 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
+ *
+ * Constraints:
+ *
+ * 	1 <= n <= 10^5
+ * 	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.
+ *
+ * Follow up:
+ *
+ * 	How can we prove that at least one duplicate number must exist in nums?
+ * 	Can you solve the problem in linear runtime complexity?
+ ******************************************************************************************************/
+
+// number[] -> number
+// return the repeated number in the given an array of integers n + 1 integers where each integer is in the range [1, n]
+
+/** Stub:
+function findDuplicate(nums: number[]): number { return 0 }
+*/
+
+/** Wrong Implementation of Floyd's Tortoise and Hare Algorithm
+function findDuplicate(nums: number[]): number {
+    if (nums.length < 3) return nums[0]
+    let d: number = 1, h: number = 2
+
+    while(nums[d] !== nums[h]) {
+        if (d === nums.length - 1) d = 0
+        else if (h + 2 > nums.length - 1) h = nums.length - h - 2
+        d++
+        h += 2
+    }
+
+    return nums[d]
+};
+*/
+
+export function findDuplicate(nums: number[]): number {
+  let slow: number = nums[0] as number;
+  let fast: number = nums[0] as number;
+
+  do {
+    slow = nums[slow] as number;
+    fast = nums[nums[fast] as number] as number;
+  } while (slow !== fast);
+
+  let ptr1: number = nums[0] as number;
+  let ptr2: number = slow;
+  while (ptr1 !== ptr2) {
+    ptr1 = nums[ptr1] as number;
+    ptr2 = nums[ptr2] as number;
+  }
+
+  return ptr1;
+}