Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array s;uch that nums[i] = nums[j]and the absolute difference between i and j is at most k.
思路:
使用一个map来存放元素，enumerate函数用于遍历序列中的元素以及它们的下标。当元素没在map中，组成一个item，index对。继续遍历。如果发现元素在map中，然后两者之差小于k，则说明存在这样的元素对。
class Solution(object):
def containsNearbyDuplicate(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: bool
"""
d = {}
for index, item in enumerate(nums):
if item in d and index - d[item] <= k:
return True
else:
d[item] = index
print d
return False
