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题目

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.

Example 1:

Input: nums = [1,2,3,1], k = 3

Output: true

注意步长为零的情况

我的想法

双指针

class Solution {
       public boolean containsNearbyDuplicate(int[] nums, int k) {
           int i = 0, j = 0;        while(i < nums.length-1){
               if(j - i == k || j == nums.length-1) {
   j = ++i; continue;}            j++;            if(nums[i] == nums[j]) return true;        }        return false;    }}

HashSet

class Solution {
       public boolean containsNearbyDuplicate(int[] nums, int k) {
           int i = 0;        Set
   
     set = new HashSet<>();        while(i < nums.length){
               if(set.contains(nums[i])) return true;            else set.add(nums[i]);            if(set.size() == k+1) set.remove(nums[i-k]);            i++;        }        return false;    }}
   

解答

HashSet的add方法是先判断set是否含有元素，可以简化solution2的步骤

public boolean containsNearbyDuplicate(int[] nums, int k) {
           Set
   
     set = new HashSet
    
     ();        for(int i = 0; i < nums.length; i++){
               if(i > k) set.remove(nums[i-k-1]);            if(!set.add(nums[i])) return true;        }        return false; }
    
   

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