算法精粹(algorithm-essentials)

感谢soulmachine@github提供内容
## Contains Duplicate II


### 描述

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`.


### 分析

维护一个HashMap, key为整数,value为下标,将数组中的元素不断添加进这个HashMap, 碰到重复时,计算二者的下标距离,如果距离小于或等于k,则返回true, 如果直到数组扫描完,距离都大于k,则返回false。


### 代码

{% if book.java %}
```java
// Contains Duplicate II
// Time Complexity: O(n), Space Complexity: O(n)
public class Solution {
public boolean containsNearbyDuplicate(int[] nums, int k) {
final Map map = new HashMap<>();
int min = Integer.MAX_VALUE;

for(int i = 0; i < nums.length; i++){
if(map.containsKey(nums[i])){
final int preIndex = map.get(nums[i]);
final int gap = i - preIndex;
min = Math.min(min, gap);
}
map.put(nums[i], i);
}
return min <= k;
}
}
```
{% endif %}