ContainsDuplicateII.java

import java.util.HashMap;

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// 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
// Example 2:

// Input: nums = [1,0,1,1], k = 1
// Output: true
// Example 3:

// Input: nums = [1,2,3,1,2,3], k = 2
// Output: false


class Solution {
  public boolean containsNearbyDuplicate(int[] nums, int k) {
    int numsLength = nums.length;
    if (numsLength == 0 || numsLength == 1) { return false; }

    HashMap<Integer, Integer> numToIndex = new HashMap<>();
    for (int i = 0; i < numsLength; i++) {
      if (numToIndex.containsKey(nums[i])) {
        int gap = i - numToIndex.get(nums[i]);
        if (gap <= k) { return true; } 
      }

      numToIndex.put(nums[i], i);
    }   

    return false;
  }
}