alive.kt

import java.text.DateFormat
import java.time.LocalDate
import java.util
import java.util.*

/*
Given a list of people with their birth and end years (all between 1900 and 2000), 
find the year with the most number of people alive.
See http://qr.ae/RAG2zH
*/

data class dates(val start:LocalDate,val end: LocalDate);
data class dateTag(val date:LocalDate,val opening:Boolean);

fun mostPeopleAlive(dates: List<dates>):Pair<Int,Int>{

    if(dates.size()==0) return Pair(0,0)

    val sortedTaggedDates=dates
            .flatMap { t-> listOf(dateTag(t.start,true),dateTag(t.end,false)) }
            .sortBy( comparator { a, b -> a.date.compareTo(b.date) })

    var opened=0
    var closed=0;
    var lastDate=sortedTaggedDates.get(0).date
    var lastYear=Int.MIN_VALUE
    var maxValue=0
    var maxYear=lastDate.getYear()

    for(i in sortedTaggedDates.indices){
        if(sortedTaggedDates[i].opening){
            opened++;
        }
        if(!sortedTaggedDates[i].opening){
            closed++;
        }

        if(opened>maxValue){
            maxValue=opened
            maxYear=sortedTaggedDates[i].date.getYear()
        }
        if(lastYear!=sortedTaggedDates[i].date.getYear()){
            lastYear=sortedTaggedDates[i].date.getYear()
            opened-=closed;
            closed=0;
        }
    }

    return Pair(maxYear,maxValue);

}

fun main(args:Array<String>){
    var dates=arrayOf(
            dates(start = LocalDate.of(2001,1,1),end = LocalDate.of(2002,5,1)),
            dates(start = LocalDate.of(2001,2,1),end = LocalDate.of(2003,1,1)),
            dates(start = LocalDate.of(2001,3,1),end = LocalDate.of(2003,3,1)),
            dates(start = LocalDate.of(2001,5,1),end = LocalDate.of(2001,10,1)),
            dates(start = LocalDate.of(2002,1,1),end = LocalDate.of(2003,2,1)),
            dates(start = LocalDate.of(2001,6,1),end = LocalDate.of(2002,3,1)),
            dates(start = LocalDate.of(2002,4,1),end = LocalDate.of(2002,7,1)),
            dates(start = LocalDate.of(2001,7,1),end = LocalDate.of(2002,6,1))
    );
    print(mostPeopleAlive(dates.asList()));
}