LeetCode Contains Duplicate II

原题链接在这里：https://leetcode.com/problems/contains-duplicate-ii/

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

Hide Tags
Array Hash
Table

Hide Similar Problems
(E) Contains Duplicate (M)
Contains Duplicate III

这道题用HashMap 来做，基本思路是检查corner case 先，然后建立一个HashMap hm, Iterate array nums from the beginning.

对于nums[i]，检查它时候在 hm 中，若不在，就加<nums[i], i>进去，key是nums[i], value 是 i.

若是nums[i] 在 hm 中，就要看当前的i 和 hm中对应nums[i]的 value 的差值是否比k大：

若是比k 大，说明不符合条件，去掉旧的pair，添加当前pair；

若是不比k大，则return true.

这里熟练几个 HashMap functions: hm.put(key, value); hm.get(key); hm,remove(key): hm.containsKey(key).

AC code:

public class Solution {
public boolean containsNearbyDuplicate(int[] nums, int k) {
if(k<1 || nums == null || nums.length<2)
return false;

HashMap<Integer, Integer> hm = new HashMap<>();

int i = 0;
while(i<nums.length){
if(!hm.containsKey(nums[i])){
hm.put(nums[i], i);
}else if((i-hm.get(nums[i])) > k ){
hm.remove(nums[i]);
hm.put(nums[i], i);
}else{
return true;
}

i++;
}

return false;

}
}