KEmptySlots.java

package array;

import java.util.TreeSet;

/**
 * Created by gouthamvidyapradhan on 01/01/2018.
 * There is a garden with N slots. In each slot, there is a flower. The N flowers will bloom one by one in N days.
 * In each day, there will be exactly one flower blooming and it will be in the status of blooming since then.

 Given an array flowers consists of number from 1 to N. Each number in the array represents the place where the
 flower will open in that day.

 For example, flowers[i] = x means that the unique flower that blooms at day i will be at position x, where i and x
 will be in the range from 1 to N.

 Also given an integer k, you need to output in which day there exists two flowers in the status of blooming, and
 also the number of flowers between them is k and these flowers are not blooming.

 If there isn't such day, output -1.

 Example 1:
 Input:
 flowers: [1,3,2]
 k: 1
 Output: 2
 Explanation: In the second day, the first and the third flower have become blooming.
 Example 2:
 Input:
 flowers: [1,2,3]
 k: 1
 Output: -1
 Note:
 The given array will be in the range [1, 20000].

 Solution: O(n log n). Maintain a tree-set of bloomed flowers and for every element in the array
 find the upper and lower bound bloomed flowers and calculate their difference with the current. If
 the difference is k return the current day, if none found then return -1

 */
public class KEmptySlots {
    /**
     * Main method
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception{
        int[] A = {1, 3, 2};
        System.out.println(new KEmptySlots().kEmptySlots(A, 2));
    }

    public int kEmptySlots(int[] flowers, int k) {
        TreeSet<Integer> set = new TreeSet<>();
        for(int i = 0; i < flowers.length; i ++){
            Integer lowerBound = set.floor(flowers[i]);
            Integer upperBound = set.ceiling(flowers[i]);
            if(lowerBound != null){
                if((Math.abs(flowers[i] - lowerBound) + 1) == k){
                    return i + 1;
                }
            } if(upperBound != null){
                if((Math.abs(flowers[i] - upperBound) + 1) == k){
                    return i + 1;
                }
            }
            set.add(flowers[i]);
        }
        return -1;
    }

}