LeetCode Find the Duplicate Number

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.

Note:

1. You must not modify the array (assume the array is read only).
2. You must use only constant, O(1) extra space.
3. Your runtime complexity should be less than O(n2).
4. There is only one duplicate number in the array, but it could be repeated more than once.

题意：给出一个数组，包含n+1个整数，由1，2，...,n组成。当中有一个重复的数，将其找出

要求：1、不能修改数组;2、只能用O(1)的空间；3、时间复杂度不能超过o(n^2)

代码如下：

class Solution
{
    public int findDuplicate(int[] nums)
    {
        if (0 == nums.length) return 0;

        int slow = 0, fast = 0;

        slow = nums[slow];
        fast = nums[nums[fast]];

        while (slow != fast)
        {
            slow = nums[slow];
            fast = nums[nums[fast]];
        }

        fast = 0;
        while (slow != fast)
        {
            slow = nums[slow];
            fast = nums[fast];
        }

        return slow;
    }
}