Minimum number of boats required to save population

Boats.java

/* File:    Boats.java
 * Created: 7/24/2019
 * Author:  Sabbir Manandhar
 *
 * Copyright (c) 2019 Hogwart Inc.
 */

import java.util.Arrays;
import java.util.Collections;

//=======================================================================================

/**
 * @author Sabbir Manandhar
 * @version 1.0
 */
public class Boats {

  /**
   * Driver method
   */
  public static void main(String[] args) {
    System.out.println(compute(new Integer[]{100, 200, 150, 80}, 200) + " == " + 3);
    System.out.println(compute(new Integer[]{30, 40, 70, 100, 200, 150, 80}, 200) + " == " + 4);
    System.out.println(compute(new Integer[]{}, 1) + " == " + 0);
    System.out.println(compute(new Integer[]{100}, 200) + " == " + 1);
    System.out.println(compute(new Integer[]{200, 10, 200, 200}, 200) + " == " + 4);
    System.out.println(compute(new Integer[]{200, 200, 10, 200, 200}, 200) + " == " + 5);
    System.out.println(compute(new Integer[]{170, 160, 30, 90}, 200) + " == " + 3);
    System.out.println(compute(new Integer[]{150, 150, 150, 30}, 200) + " == " + 3);
  } // main

  //-----------------------------------------------------------------------------------------------

  /**
   * Computes number of boats required
   * @param weights array of weights of population
   * @param limit weight limit of each boat
   * @return number of boats needed
   *
   */
  public static int compute(Integer[] weights, int limit) {
    if(weights.length == 0) return 0;

    Arrays.sort(weights, Collections.reverseOrder());
    boolean[] used = new boolean[weights.length];
    int boats = 0;
    for(int idx = 0; idx < weights.length; idx++) {
      if (used[idx]) continue;

      if (weights[idx] == limit) {
        boats++;
        continue;
      }

      int pair = findPair(weights, used, limit - weights[idx], idx+1, weights.length-1);
      if (pair > -1) {
        used[pair] = true;
      }
      boats++;
    }
    return boats;
  } // compute


  /**
   * Find pairing for the limit provided
   * @param weights
   * @param used
   * @param limit
   * @param lo
   * @param hi
   * @return
   */
  private static int findPair(Integer[] weights, boolean[] used, int limit, int lo, int hi) {
    int lastValid = -1;
    for (int i = hi; i >= lo; i--) {
      if (!used[i]) {
        if (weights[i] == limit) {
          return i;
        } else if (weights[i] < limit) {
          lastValid = i;
        } else {
          return lastValid;
        }
      } else {
        continue;
      }
    }
    return lastValid;
  } // findPair

} // Boats