LeetCode 219. Contains Duplicate II（检查重复）

原题网址：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 difference between i and j is
at most k.

方法一：使用哈希映射。

public class Solution {
public boolean containsNearbyDuplicate(int[] nums, int k) {
if (nums == null || nums.length <= 1) return false;
Map<Integer, Integer> map = new HashMap<>();
map.put(nums[0], 0);
for(int i=1; i<nums.length; i++) {
Integer prev = map.get(nums[i]);
if (prev != null && i-prev<=k) return true;
map.put(nums[i], i);
}
return false;
}
}

方法二：使用哈希集合。

public class Solution {
public boolean containsNearbyDuplicate(int[] nums, int k) {
if (nums == null || nums.length <= 1 || k <= 0) return false;
Set<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;
}
}