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 difference between i and j is at most k.

思路: 218的变体, 可以用HashTable来记录元素。我们可以用HashMap记为map, 如果map中存在则获得之前元素的位置pre, 用当前元素的位置 – 之前元素的位置 <= k。 别忘了更新走过的元素位置。

注意case [1, 0, 1, 1] k=1情况

public class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        if(nums == null || nums.length < 2 || k == 0) return false;

        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        for (int i = 0; i < nums.length; i++) {
            if (map.containsKey(nums[i])) {
                int pre = map.get(nums[i]);
                if (i - pre <= k) return true;
            map.put(nums[i], i);
        return false;

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