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

// Contains Duplicate II
// Time Complexity: O(n), Space Complexity: O(n)
public class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        final Map<Integer, Integer> 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;
    }
}