287. Find the Duplicate Number

Medium (Trung bình) Python 🔗 Xem trên LeetCode

📋 Đề Bài

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 <= 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.

 

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?

🧠 Thuật Toán & Kỹ Thuật

Sorting (Sắp xếp)
⏱️ Thời gian O(n log n)
💾 Không gian O(n)

💻 Lời Giải

Python 0287-find-the-duplicate-number.py 
class Solution:
    def findDuplicate(self, nums: List[int]) -> int:
        nums.sort()
        n = len(nums)
        
        for i in range(1, n):
            if nums[i - 1] == nums[i]:
                return nums[i]
            
        return -1