219. Contains Duplicate II

Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k.

Example 1:

Input: nums = [1,2,3,1], k = 3
Output: true

Example 2:

Input: nums = [1,0,1,1], k = 1
Output: true

Example 3:

Input: nums = [1,2,3,1,2,3], k = 2
Output: false

解题要点：

保持一个k长度的set，检测里面是否有重复数。

class Solution(object):
    def containsNearbyDuplicate(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: bool
        """
        s = set()
        for i in range(len(nums)):
            if nums[i] in s:
                return True
            s.add(nums[i])
            if(len(s) > k):
                s.remove(nums[i - k])
        return False

直接用dict记录index和value，然后检测差值是否在k值内。

class Solution(object):
    def containsNearbyDuplicate(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: bool
        """
        mydict = dict()
        for i, v in enumerate(nums):
            if v in mydict and i - mydict[v] <= k:
                return True
            mydict[v] = i
        return False