287. Find the Duplicate Number

Leetcode Array Two Pointers Binary Search

Given an array nums containing $n + 1$ integers where each integer is between 1 and $n$ (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.

Example 1:

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

Example 2:

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

Note:

• You must not modify the array (assume the array is read only).
• You must use only constant, O(1) extra space.
• Your runtime complexity should be less than $O(n^2)$.
• There is only one duplicate number in the array, but it could be repeated more than once.

分析