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287. Find The Duplicate Number

Array Two Pointers Binary Search Bit Manipulation

Problem - Find The Duplicate Number

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.

 

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?

Solutions

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class Solution:
    def findDuplicate(self, nums: List[int]) -> int:
        def keyfunc(i: int) -> bool:
            return sum(x <= i for x in nums) > i

        return bisect_left(range(len(nums)), True, key=keyfunc)

Submission Stats:

  • Runtime: 259 ms (5.04%)
  • Memory: 29.1 MB (98.73%)