## 题目

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:

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

Example 2:

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

**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.

## 思路

通过重复元素的索引找到重复元素。

## 代码

1 | class Solution(object): |