Problem:
Score : 100 points

Problem Statement

There is a tree with N vertices, numbered 1, 2, \ldots, N.
For each i (1 \leq i \leq N - 1), the i-th edge connects Vertex x_i and y_i.

Taro has decided to paint each vertex in white or black.
Here, it is not allowed to paint two adjacent vertices both in black.

Find the number of ways in which the vertices can be painted, modulo 10^9 + 7.

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq x_i, y_i \leq N

The given graph is a tree.

Input

Input is given from Standard Input in the following format:

N
x_1 y_1
x_2 y_2
:
x_{N - 1} y_{N - 1}

Output

Print the number of ways in which the vertices can be painted, modulo 10^9 + 7.

Sample Input 1

3
1 2
2 3

Sample Output 1

5

There are five ways to paint the vertices, as follows:

Sample Input 2

4
1 2
1 3
1 4

Sample Output 2

9

There are nine ways to paint the vertices, as follows:

Sample Input 3

1

Sample Output 3

2

Sample Input 4

10
8 5
10 8
6 5
1 5
4 8
2 10
3 6
9 2
1 7

Sample Output 4

157

Solution in Rust (1.15.1) (judge verdict: Wrong Answer)

#![allow(unused_imports)]
#![allow(unused_macros)]
use std::cmp::{ min, max };

macro_rules! ewriteln {
    ($($args:expr),*) => { let _ = writeln!(&mut std::io::stderr(), $($args),*); };
}
macro_rules! trace {
    ($x:expr) => { ewriteln!(">>> {} = {:?}", stringify!($x), $x) };
    ($($xs:expr),*) => { trace!(($($xs),*)) }
}
macro_rules! put {
    ($x:expr) => { println!("{}", $x) };
    ($x:expr, $($xs:expr),*) => { print!("{} ", $x); put!($($xs),*) }
}

const M: i64 = 1_000_000_007;

fn main() {
    let mut sc = Scanner::new();
    let n: usize = sc.cin();
    let mut tree = vec![vec![]; n];
    for _ in 1..n {
        let x = sc.cin::<usize>()-1;
        let y = sc.cin::<usize>()-1;
        tree[x].push(y);
        tree[y].push(x);
    }

    let mut memo = vec![vec![0; 2]; n];   // [n][0] = n is WHITE, [n][1] = BLACK
    let mut stack = vec![];
    stack.push((true, 0));
    let mut used = vec![false; n];
    while let Some((d, u)) = stack.pop() {
        used[u] = true;
        if d {
            if tree[u].len() == 0 {
                memo[u][0] = 1;
                memo[u][1] = 1;
            } else {
                stack.push((false, u));
                let mut vs = vec![];
                for &v in tree[u].iter() {
                    if !used[v] {
                        vs.push(v);
                        stack.push((true, v));
                    }
                }
                tree[u] = vs;
            }
        } else {
            let mut white = 1;
            let mut black = 1;
            for &v in tree[u].iter() {
                black = (black * memo[v][0]) % M;
                white = (white * (memo[v][0] + memo[v][1])) % M;
            }
            memo[u][0] = white;
            memo[u][1] = black;
        }
    }

    put!(memo[0][0] + memo[0][1]);

}

use std::io::{self, Write};
use std::str::FromStr;
use std::collections::VecDeque;

struct Scanner { stdin: io::Stdin, buffer: VecDeque<String>, }
impl Scanner {
    fn new() -> Scanner { Scanner { stdin: io::stdin(), buffer: VecDeque::new() } }
    fn cin<T: FromStr>(&mut self) -> T {
        while self.buffer.len() == 0 {
            let mut line = String::new();
            let _ = self.stdin.read_line(&mut line);
            for w in line.split_whitespace() {
                self.buffer.push_back(String::from(w));
            }
        }
        self.buffer.pop_front().unwrap().parse::<T>().ok().unwrap()
    }
}