leetcode287 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.
Example 1:
Input: [1,3,4,2,2]
Output: 2
Example 2:
Input: [3,1,3,4,2]
Output: 3
"""
"""
解法一：
这道题竟然可以用快慢指针法！！！
与leetcode142类似。https://www.cnblogs.com/yawenw/p/12324170.html
因此找环 找重复值 都可以考虑用快慢指针法
"""
class Solution1:
    def findDuplicate(self, nums):
        if not nums:
            return -1
        slow = nums[0]
        fast = nums[nums[0]]
        while slow != fast:
            slow = nums[slow]
            fast = nums[nums[fast]]
        fast = 0
        while slow != fast:
            fast = nums[fast]
            slow = nums[slow]
        return slow

"""
解法二：时间复杂度高的解法
"""
class Solution2:
    def findDuplicate(self, nums):
        for i in range(len(nums)):
            if nums[i] in nums[i+1:]:
                return nums[i]