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 Rust (1.15.1) (judge verdict: Accepted)

//! ----------------------------------------------
//! Framework <https://github.com/vain0x/procon>
//!
//! See the bottom of file for solution.
//! ----------------------------------------------

#![allow(unused_imports)]
#![allow(non_snake_case)]

use std::cell::RefCell;
use std::cmp::{max, min, Ordering};
use std::collections::*;
use std::fmt::{Debug, Display, Formatter, Write as FmtWrite};
use std::io::{stderr, stdin, BufRead, Write};
use std::mem::{replace, swap};
use std::ops::*;
use std::rc::Rc;

/// Print values to standard error if debug mode.
#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), stderr());
            writeln!(err, "\x1B[33m{}\x1B[0m = {:?}", e, $e).unwrap()
        })*
    };
}

/// Read from standard input and parse each word.
/// - `read!(T, U, ..)` parses a line as a tuple of words.
/// - `read![[T]]` parses a line as an array of words.
/// - `read![..; N]` parses `N` lines, using `read!(..)` repeatedly.
#[allow(unused_macros)]
macro_rules! read {
    ([$t:ty] ; $n:expr) =>
        ((0..$n).map(|_| read!([$t])).collect::<Vec<_>>());
    ($($t:ty),+ ; $n:expr) =>
        ((0..$n).map(|_| read!($($t),+)).collect::<Vec<_>>());
    ([$t:ty]) =>
        (rl().split_whitespace().map(|w| w.parse().unwrap()).collect::<Vec<$t>>());
    ($($t:ty),*) => {{
        let buf = rl();
        let mut w = buf.split_whitespace();
        ($(w.next().unwrap().parse::<$t>().unwrap()),*)
    }};
}

/// Read a line from standard input.
#[allow(dead_code)]
fn rl() -> String {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();

    #[allow(deprecated)]
    buf.trim_right().to_owned()
}

// -----------------------------------------------
// Solution
// -----------------------------------------------

pub struct UnionFind {
    nodes: Vec<UnionFindNode>,
}

enum UnionFindNode {
    Root { size: usize },
    Child { parent: RefCell<usize> },
}

impl UnionFind {
    /// Create an union find with `size` vertices.
    pub fn new(size: usize) -> Self {
        UnionFind {
            nodes: (0..size)
                .map(|_| UnionFindNode::Root { size: 1 })
                .collect::<Vec<_>>(),
        }
    }

    /// Get the root index and its component size.
    fn root_node(&self, v: usize) -> (usize, usize) {
        match &self.nodes[v] {
            &UnionFindNode::Root { size } => (v, size),
            &UnionFindNode::Child { parent: ref p } => {
                let (u, size) = self.root_node(*p.borrow());
                // Path compression.
                *p.borrow_mut() = u;
                (u, size)
            }
        }
    }

    /// Get the root index.
    pub fn root(&self, v: usize) -> usize {
        self.root_node(v).0
    }

    /// Get the size of component.
    pub fn size(&self, v: usize) -> usize {
        self.root_node(v).1
    }

    /// Determine if two vertices are in the same component.
    pub fn connects(&self, u: usize, v: usize) -> bool {
        self.root(u) == self.root(v)
    }

    /// Merge components by adding an edge between the two vertices.
    pub fn merge(&mut self, u: usize, v: usize) {
        let (u, u_size) = self.root_node(u);
        let (v, v_size) = self.root_node(v);

        if u == v {
            return;
        }

        if u_size < v_size {
            self.merge(v, u);
            return;
        }

        self.nodes[v] = UnionFindNode::Child {
            parent: RefCell::new(u),
        };
        self.nodes[u] = UnionFindNode::Root {
            size: u_size + v_size,
        };
    }
}

fn main() {
    let (N, M) = read!(usize, usize);
    let T = read![usize, usize, i32; M];

    let mut uf = UnionFind::new(N);
    for (x, y, _) in T {
        uf.merge(x - 1, y - 1);
    }
    let count = uf
        .nodes
        .iter()
        .filter(|node| match node {
            &&UnionFindNode::Root { .. } => true,
            _ => false,
        })
        .count();

    println!("{}", count)
}