## CODING

# Day 27: The “Find the Duplicate Number” Problem

**Problem:**

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