Problem:
Score : 300 points

Problem Statement

There is an empty array.
The following N operations will be performed to insert integers into the array.
In the i-th operation (1≤i≤N), b_i copies of an integer a_i are inserted into the array.
Find the K-th smallest integer in the array after the N operations.
For example, the 4-th smallest integer in the array \{1,2,2,3,3,3\} is 3.

Constraints

1≤N≤10^5

1≤a_i,b_i≤10^5

1≤K≤b_1…+…b_n

All input values are integers.

Input

Input is given from Standard Input in the following format:

N K
a_1 b_1
:
a_N b_N

Output

Print the K-th smallest integer in the array after the N operations.

Sample Input 1

3 4
1 1
2 2
3 3

Sample Output 1

3

The resulting array is the same as the one in the problem statement.

Sample Input 2

10 500000
1 100000
1 100000
1 100000
1 100000
1 100000
100000 100000
100000 100000
100000 100000
100000 100000
100000 100000

Sample Output 2

1

Solution in Scala (2.11.7) (judge verdict: Accepted)

import scala.collection.mutable.HashMap
import scala.annotation.tailrec

object Main extends App {
  val Array(n, k) = io.StdIn.readLine.split(" ").map(_.toLong)
  val map = HashMap.empty[Int, Long]
  Iterator.continually(io.StdIn.readLine)
    .take(n.toInt)
    .map(_.split(" "))
    .foreach(e => {
      val key   = e(0).toInt
      val value = e(1).toLong
      if(!map.contains(key)) map += key -> value
      else map(key) += value
    })

  def f(map:HashMap[Int, Long], k:Long):Int = {
    val ite = map.keys.toList.sorted.iterator

    @tailrec
    def rec(acc:Long, key:Int, k:Long ):Int = {
      val res = acc + map(key)
      if(res >= k) key
      else rec(res, ite.next, k)
    }

    rec(0L, ite.next, k)
  }

  println(f(map, k))
}