QuestionC.java

package Q16_10_Living_People;

import java.util.Arrays;
import java.util.Random;

public class QuestionC {
	public static int maxAliveYear(Person[] people, int min, int max) {
		int[] births = getSortedYears(people, true);
		int[] deaths = getSortedYears(people, false);

		int birthIndex = 0;
		int deathIndex = 0;		
		int currentlyAlive = 0;
		int maxAlive = 0;
		int maxAliveYear = min;
		
		/* Walk through arrays. */
		while (birthIndex < births.length) {
			if (births[birthIndex] <= deaths[deathIndex]) {
				currentlyAlive++; // include birth 
				if (currentlyAlive > maxAlive) { 
					maxAlive = currentlyAlive;
					maxAliveYear = births[birthIndex];
				}
				birthIndex++; // move birth index
			} else if (births[birthIndex] > deaths[deathIndex]) {
				currentlyAlive--; // include death
				deathIndex++; // move death index
			}			
		}
		
		return maxAliveYear;
	}
	
	/* Copy birth years or death years (depending on the value of copyBirthYear)
	 * into integer array, then sort array. */
	public static int[] getSortedYears(Person[] people, boolean copyBirthYear) {
		int[] years = new int[people.length];
		for (int i = 0; i < people.length; i++) {
			years[i] = copyBirthYear ? people[i].birth : people[i].death;
		}
		Arrays.sort(years);
		return years;
	}
	
	public static void main(String[] args) {
		int n = 3;
		int first = 1900;
		int last = 2000;
		Random random = new Random();
		Person[] people = new Person[n];
		for (int i = 0; i < n; i++) {
			int birth = first + random.nextInt(last - first);
			int death = birth + random.nextInt(last - birth);
			people[i] = new Person(birth, death);
			System.out.println(birth + ", " + death);
		}
		int year = maxAliveYear(people, first, last);
		System.out.println(year);
	}

}