219. 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 absolute difference between i and j is at most k.

给定一个数组，和一个整数k，判断该数组中是否存在不同下标的 i 和 j 两个元素，使得 nums[i] = nums[j]，且 i 和 j 的差不超过k。

    public boolean containsNearbyDuplicate(int[] nums, int k) {
        if (nums == null || nums.length == 0)
            return false;
        Map<Integer, List<Integer>> numberMap = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            List<Integer> indexs = numberMap.getOrDefault(nums[i], new ArrayList<>());
            indexs.add(i);
            numberMap.put(nums[i], indexs);
        }
        for (Map.Entry<Integer,List<Integer>> entry:numberMap.entrySet())
        {
            if (entry.getValue().size()>1)
            {
                List<Integer> indexs = entry.getValue();
                for (int i=indexs.size()-1; i>0;i--)
                {
                    if(indexs.get(i) - indexs.get(i-1) <= k)
                        return true;
                }
            }
        }
        return false;        
    }