【LeetCode】219. Contains Duplicate II

Difficulty:easy

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Description

https://leetcode.com/problems/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 absolutedifference 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

Intuition

hashSet

 

Solution

    public boolean containsNearbyDuplicate(int[] nums, int k) {
        if(nums == null)
            return false;
        HashSet<Integer> set = new HashSet<>();
        for(int i=0; i<nums.length;i++){
            if(i>k)
                set.remove(nums[i-k-1]);
            if(!set.add(nums[i]))
                return true;
        }
        return false;
    }

　　

Complexity

Time complexity : O(n)

Space complexity : O(k)

 

What I've learned

1.  set.add(e) returns false if the set already contains the specified element. 

 

 More:【目錄】LeetCode Java實現