Problem:
Score : 500 points

Problem Statement

There are N cards placed face down in a row. On each card, an integer 1 or 2 is written.

Let A_i be the integer written on the i-th card.

Your objective is to guess A_1, A_2, ..., A_N correctly.

You know the following facts:

For each i = 1, 2, ..., M, the value A_{X_i} + A_{Y_i} + Z_i is an even number.

You are a magician and can use the following magic any number of times:

Magic: Choose one card and know the integer A_i written on it. The cost of using this magic is 1.

What is the minimum cost required to determine all of A_1, A_2, ..., A_N?

It is guaranteed that there is no contradiction in given input.

Constraints

All values in input are integers.

2 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq X_i < Y_i \leq N

1 \leq Z_i \leq 100

The pairs (X_i, Y_i) are distinct.

There is no contradiction in input. (That is, there exist integers A_1, A_2, ..., A_N that satisfy the conditions.)

Input

Input is given from Standard Input in the following format:

N M
X_1 Y_1 Z_1
X_2 Y_2 Z_2
\vdots
X_M Y_M Z_M

Output

Print the minimum total cost required to determine all of A_1, A_2, ..., A_N.

Sample Input 1

3 1
1 2 1

Sample Output 1

2

You can determine all of A_1, A_2, A_3 by using the magic for the first and third cards.

Sample Input 2

6 5
1 2 1
2 3 2
1 3 3
4 5 4
5 6 5

Sample Output 2

2

Sample Input 3

100000 1
1 100000 100

Sample Output 3

99999

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

import java.util.Scanner

import scala.collection.mutable.ArrayBuffer

object Main {

  class UnionFind(val n: Int) {

    sealed trait Node

    final case class Root(count: Int, rank: Int) extends Node

    final case class NonRoot(parentIndex: Int) extends Node

    // TODO ArrayBufferではなくArrayでいいはず
    private val nodes: ArrayBuffer[Node] = ArrayBuffer.fill(n)(Root(count = 1, rank = 0))

    private def rootNode(index: Int): (Int, Root) = {
      nodes(index) match {
        case root: Root => (index, root) // nodes(index) == root
        case nonRoot: NonRoot =>
          val (rootIndex, root) = rootNode(nonRoot.parentIndex)
          nodes(index) = NonRoot(parentIndex = rootIndex) // 経路圧縮
          (rootIndex, root)
      }
    }

    def numComponents(): Int = nodes.count(p = node => node.isInstanceOf[Root])

    private def root(index: Int): Int = rootNode(index)._1

    def sameCount(x: Int): Int = rootNode(x)._2.count

    def same(x: Int, y: Int): Boolean = root(x) == root(y)


    def unite(x: Int, y: Int): Unit = {
      if (same(x, y)) return

      val (xRootIndex, xRoot) = rootNode(x)
      val (yRootIndex, yRoot) = rootNode(y)

      if (xRoot.rank < yRoot.rank) {
        // xRootの親をyRootとする
        nodes(xRootIndex) = NonRoot(parentIndex = yRootIndex)
        nodes(yRootIndex) = yRoot.copy(count = xRoot.count + yRoot.count)
      } else {
        // yRootの親をxRootとする
        nodes(yRootIndex) = NonRoot(parentIndex = xRootIndex)
        val nextXRootRank = xRoot.rank + (if (xRoot.rank == yRoot.rank) 1 else 0)
        nodes(xRootIndex) = Root(count = xRoot.count + yRoot.count, rank = nextXRootRank)
      }
    }

  }

  case class Magic(x: Int, y: Int, z: Long)

  case class NextInfo(v: Int, w: Long)

  def read() = {
    val sc = new Scanner(System.in)
    val n, m = sc.nextInt()
    // 0-index化
    val magics = IndexedSeq.fill(m)(
      Magic(sc.nextInt() - 1, sc.nextInt() - 1, sc.nextLong()))
    (n, m, magics)
  }


  def solve(n: Int, m: Int, magics: IndexedSeq[Magic]): Int = {
    val uf = new UnionFind(n)
    for (magic <- magics) {
      uf.unite(magic.x, magic.y)
    }
    uf.numComponents()
  }

  def main(args: Array[String]): Unit = {
    val (n, m, magics) = read()
    val result = solve(n, m, magics)
    println(result)
  }
}