217 Contains duplicates

Original Description: Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct.

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• 要求： 给一个数组，判断其是否中是否含有重复元素

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• 返回： True/False

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• 例子：
  • input: [1,2,3,1]
  • output: True

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Solution

option 1: 如果set()的长度小于数组长度，则有重复;（code in comment）；
option 2: 使用dictionary, 遍历数组，判断是否在dict中。

class Solution(object):
    def containsDuplicate(self, nums):
        """
        :type nums: List[int]
        :rtype: bool
        """
        ##### sol1: use set()
        # if len(set(nums)) < len(nums):
        #     return True
        # else:
        #     return False
        
        ##### sol2: use dict()
        c = dict()
        flag = False
        for n in nums:
            if n not in c: 
                c[n] = 1
            else:
                flag = True
        return flag