203. Find the Duplicate Number

MediumTwo Pointers

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.

Examples

Input: [1,3,4,2,2]

Output: 2

Explanation: Following index pointers from 0 cycles at value 2, the duplicate.

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.
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