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 difference between i and j is at most k.


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。


// 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++){
                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;

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