QueueReconstructionByHeight.java

package greedy;

import java.util.Arrays;
import java.util.LinkedList;

/**
 * Created by gouthamvidyapradhan on 29/06/2017.
 * Suppose you have a random list of people standing in a queue. Each person is described by a pair of integers (h, k), where h is the height of the person and k is the number of people in front of this person who have a height greater than or equal to h. Write an algorithm to reconstruct the queue.
 * <p>
 * Note:
 * The number of people is less than 1,100.
 * <p>
 * Example
 * <p>
 * Input:
 * [[7,0], [4,4], [7,1], [5,0], [6,1], [5,2]]
 * <p>
 * Output:
 * [[5,0], [7,0], [5,2], [6,1], [4,4], [7,1]]
 */
public class QueueReconstructionByHeight {
    public static void main(String[] args) throws Exception {
        int[][] A = {{7, 0}, {4, 4}, {7, 1}, {5, 0}, {6, 1}, {5, 2}};
        int[][] r = new QueueReconstructionByHeight().reconstructQueue(A);
        for (int[] i : r) {
            System.out.println(i[0] + " " + i[1]);
        }
    }

    public int[][] reconstructQueue(int[][] people) {
        Arrays.sort(people, ((o1, o2) -> (o2[0] - o1[0] == 0) ? o1[1] - o2[1] : o2[0] - o1[0]));
        LinkedList<int[]> list = new LinkedList<>();
        for (int[] p : people)
            list.add(p[1], p);
        int[][] result = new int[people.length][2];
        for (int i = 0, l = list.size(); i < l; i++)
            result[i] = list.get(i);
        return result;
    }
}