ContainsDuplicatesII219.java

/**
 * 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.
 */


import java.util.HashSet;
import java.util.Set;
import java.util.HashMap;
import java.util.Map;


public class ContainsDuplicatesII219 {
    // too slow
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        if (nums.length < 2) {
          return false;
        }

        for (int i = 0; i < nums.length; i++) {
          int numI = nums[i];
          for (int j = i + 1; j < nums.length && j - i <= k; j++) {
            int numJ = nums[j];
            if (numI == numJ) {
              return true;
            }
          }
        }
        return false;
    }

    public boolean containsNearbyDuplicate2(int[] nums, int k) {
        if (nums.length < 2) {
          return false;
        }

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

        return false;
    }

    /**
     * https://discuss.leetcode.com/topic/15305/simple-java-solution
     */
    public boolean containsNearbyDuplicate3(int[] nums, int k) {
        Set<Integer> set = new HashSet<Integer>();
        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;
    }


    public static void main(String[] args) {
        ContainsDuplicatesII219 cd2 = new ContainsDuplicatesII219();

        System.out.println(cd2.containsNearbyDuplicate2(new int[]{5, 8, 2, 10, 5}, 4));
        System.out.println(cd2.containsNearbyDuplicate2(new int[]{5, 8, 2, 10}, 1));
    }
}