LeetCode 219. Contains Duplicate II

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

题目：

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.

题解：

是Contains Duplicate的进阶版题目，类似题目还有Contains Duplicate III.

建立一个HashMap hm, key是nums[i], value 是 index i.

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

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).

Time Complexity: O(n). Space: O(n).

AC Java:

 1 public class Solution {
 2     public boolean containsNearbyDuplicate(int[] nums, int k) {
 3         if(nums == null || nums.length == 0){
 4             return false;
 5         }
 6         HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>();
 7         for(int i = 0; i<nums.length; i++){
 8             if(!hm.containsKey(nums[i])){
 9                 hm.put(nums[i],i);
10             }else if(i - hm.get(nums[i]) > k){
11                 hm.put(nums[i], i);
12             }else{
13                 return true;
14             }
15         }
16         return false;
17     }
18 }

AC C++:

 1 class Solution {
 2 public:
 3     bool containsNearbyDuplicate(vector<int>& nums, int k) {
 4         unordered_map<int, int> map;
 5         for(int i = 0; i < nums.size(); i++){
 6             if(map.find(nums[i]) != map.end() && i - map[nums[i]] <= k){
 7                 return true;
 8             }
 9 
10             map[nums[i]] = i;
11         }
12 
13         return false;
14     }
15 };