Problem:
Score : 900 points

Problem Statement

We have an undirected weighted graph with N vertices and M edges.
The i-th edge in the graph connects Vertex U_i and Vertex V_i, and has a weight of W_i.
Additionally, you are given an integer X.

Find the number of ways to paint each edge in this graph either white or black such that the following condition is met, modulo 10^9 + 7:

The graph has a spanning tree that contains both an edge painted white and an edge painted black. Furthermore, among such spanning trees, the one with the smallest weight has a weight of X.

Here, the weight of a spanning tree is the sum of the weights of the edges contained in the spanning tree.

Constraints

1 \leq N \leq 1 000

1 \leq M \leq 2 000

1 \leq U_i, V_i \leq N (1 \leq i \leq M)

1 \leq W_i \leq 10^9 (1 \leq i \leq M)

If i \neq j, then (U_i, V_i) \neq (U_j, V_j) and (U_i, V_i) \neq (V_j, U_j).

U_i \neq V_i (1 \leq i \leq M)

The given graph is connected.

1 \leq X \leq 10^{12}

All input values are integers.

Input

Input is given from Standard Input in the following format:

N M
X
U_1 V_1 W_1
U_2 V_2 W_2
:
U_M V_M W_M

Output

Print the answer.

Sample Input 1

3 3
2
1 2 1
2 3 1
3 1 1

Sample Output 1

6

Sample Input 2

3 3
3
1 2 1
2 3 1
3 1 2

Sample Output 2

2

Sample Input 3

5 4
1
1 2 3
1 3 3
2 4 6
2 5 8

Sample Output 3

0

Sample Input 4

8 10
49
4 6 10
8 4 11
5 8 9
1 8 10
3 8 128773450
7 8 10
4 2 4
3 4 1
3 1 13
5 2 2

Sample Output 4

4

Solution in Rust (1.42.0) (judge verdict: Accepted)

use crate::mod_int::ModInt;
use std::cmp::{max, min};
use std::collections::VecDeque;

const MOD: u64 = 1e9 as u64 + 7;

fn main() {
    let (r, w) = (std::io::stdin(), std::io::stdout());
    let mut sc = IO::new(r.lock(), w.lock());

    let n: usize = sc.read();
    let m: usize = sc.read();
    let x: i64 = sc.read();

    let mut edges = vec![];
    for _ in 0..m {
        let u = sc.read::<usize>() - 1;
        let v = sc.read::<usize>() - 1;
        let w: i64 = sc.read();
        edges.push((w, u, v));
    }
    edges.sort();

    let mut minimum_spanning_tree = vec![vec![]; n];
    let mut used = vec![false; m];
    let mut uf = UnionFind::new(n);
    let mut sum = 0;
    for (i, &(w, u, v)) in edges.iter().enumerate() {
        if uf.find(u) != uf.find(v) {
            uf.unite(u, v);
            minimum_spanning_tree[u].push((v, w));
            minimum_spanning_tree[v].push((u, w));
            used[i] = true;
            sum += w;
        }
    }

    let longest = (0..n)
        .map(|start| {
            let mut longest = vec![0; n];
            dfs(start, start, &minimum_spanning_tree, &mut longest);
            longest
        })
        .collect::<Vec<_>>();
    let requires = x - sum;
    if requires < 0 {
        println!("0");
        return;
    }

    let mut upper = 0;
    let mut equal = 0;
    for (i, &(w, u, v)) in edges.iter().enumerate() {
        if used[i] {
            continue;
        }
        let difference = w - longest[u][v];
        if difference == requires {
            equal += 1;
        } else if difference > requires {
            upper += 1;
        }
    }

    if requires == 0 {
        let ans1 = (m_int(2).pow(equal) - 1) * 2 * m_int(2).pow(upper);
        let ans2 = (m_int(2).pow(n as u64 - 1) - 2) * m_int(2).pow((m - n + 1) as u64);
        println!("{}", (ans1 + ans2).value());
    } else {
        let ans = (m_int(2).pow(equal) - 1) * 2 * m_int(2).pow(upper);
        println!("{}", ans.value());
    }
}

fn m_int(v: u64) -> ModInt<u64> {
    ModInt::new(v, MOD)
}

pub mod mod_int {
    use std::ops::{
        Add, AddAssign, BitAnd, Div, DivAssign, Mul, MulAssign, RemAssign, ShrAssign, Sub,
        SubAssign,
    };

    pub struct ModInt<T> {
        v: T,
        m: T,
    }

    impl<T> ModInt<T>
    where
        T: Copy,
    {
        pub fn value(&self) -> T {
            self.v
        }
        pub fn modulo(&self) -> T {
            self.m
        }
    }

    impl<T> ModInt<T> {
        fn new_unchecked(v: T, modulo: T) -> Self {
            Self { v, m: modulo }
        }
    }

    impl<T> ModInt<T>
    where
        T: Copy + RemAssign + PartialOrd,
    {
        pub fn new(mut v: T, modulo: T) -> Self {
            if v >= modulo {
                v %= modulo;
            }
            Self::new_unchecked(v, modulo)
        }
    }

    impl<T> ModInt<T>
    where
        T: Copy
            + Sub<Output = T>
            + ShrAssign
            + BitAnd<Output = T>
            + PartialEq
            + PartialOrd
            + Div<Output = T>
            + RemAssign,
        ModInt<T>: MulAssign,
    {
        pub fn pow(self, e: T) -> Self {
            let zero = self.modulo() - self.modulo();
            let one = self.modulo() / self.modulo();
            let mut e = e;
            let mut result = Self::new_unchecked(one, self.modulo());
            let mut cur = self;
            while e > zero {
                if e & one == one {
                    result *= cur;
                }
                e >>= one;
                cur *= cur;
            }
            result
        }
    }

    impl<T> Copy for ModInt<T> where T: Copy {}
    impl<T> Clone for ModInt<T>
    where
        T: Copy,
    {
        fn clone(&self) -> Self {
            Self::new_unchecked(self.value(), self.modulo())
        }
    }

    impl<T> Add<T> for ModInt<T>
    where
        T: AddAssign + SubAssign + RemAssign + Copy + PartialOrd,
    {
        type Output = Self;
        fn add(self, mut rhs: T) -> Self::Output {
            if rhs >= self.modulo() {
                rhs %= self.modulo();
            }
            rhs += self.value();
            if rhs >= self.modulo() {
                rhs -= self.modulo();
            }
            Self::new_unchecked(rhs, self.modulo())
        }
    }

    impl<T> Sub<T> for ModInt<T>
    where
        T: AddAssign + SubAssign + RemAssign + Copy + PartialOrd,
    {
        type Output = Self;
        fn sub(self, mut rhs: T) -> Self::Output {
            if rhs >= self.modulo() {
                rhs %= self.modulo();
            }

            let mut result = self.value();
            result += self.modulo();
            result -= rhs;

            if result >= self.modulo() {
                result -= self.modulo();
            }
            Self::new_unchecked(result, self.modulo())
        }
    }

    impl<T> Mul<T> for ModInt<T>
    where
        T: MulAssign + RemAssign + Copy + PartialOrd,
    {
        type Output = Self;
        fn mul(self, mut rhs: T) -> Self::Output {
            if rhs >= self.modulo() {
                rhs %= self.modulo();
            }
            rhs *= self.value();
            rhs %= self.modulo();
            Self::new_unchecked(rhs, self.modulo())
        }
    }

    impl<T> Add<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Add<T, Output = ModInt<T>>,
    {
        type Output = Self;
        fn add(self, rhs: ModInt<T>) -> Self::Output {
            self + rhs.value()
        }
    }
    impl<T> Sub<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Sub<T, Output = ModInt<T>>,
    {
        type Output = Self;
        fn sub(self, rhs: ModInt<T>) -> Self::Output {
            self - rhs.value()
        }
    }
    impl<T> Mul<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Mul<T, Output = ModInt<T>>,
    {
        type Output = Self;
        fn mul(self, rhs: ModInt<T>) -> Self::Output {
            self * rhs.value()
        }
    }
    impl<T> Div<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Div<T, Output = ModInt<T>>,
    {
        type Output = Self;
        fn div(self, rhs: ModInt<T>) -> Self::Output {
            self / rhs.value()
        }
    }

    impl<T> AddAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Add<T, Output = ModInt<T>>,
    {
        fn add_assign(&mut self, other: T) {
            *self = *self + other;
        }
    }
    impl<T> AddAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Add<ModInt<T>, Output = ModInt<T>>,
    {
        fn add_assign(&mut self, other: ModInt<T>) {
            *self = *self + other;
        }
    }

    impl<T> SubAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Sub<T, Output = ModInt<T>>,
    {
        fn sub_assign(&mut self, other: T) {
            *self = *self - other;
        }
    }

    impl<T> SubAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Sub<ModInt<T>, Output = ModInt<T>>,
    {
        fn sub_assign(&mut self, other: ModInt<T>) {
            *self = *self - other;
        }
    }

    impl<T> DivAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Div<T, Output = ModInt<T>>,
    {
        fn div_assign(&mut self, rhs: T) {
            *self = *self / rhs
        }
    }
    impl<T> DivAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Div<ModInt<T>, Output = ModInt<T>>,
    {
        fn div_assign(&mut self, rhs: ModInt<T>) {
            *self = *self / rhs
        }
    }

    impl<T> MulAssign<T> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Mul<T, Output = ModInt<T>>,
    {
        fn mul_assign(&mut self, rhs: T) {
            *self = *self * rhs;
        }
    }

    impl<T> MulAssign<ModInt<T>> for ModInt<T>
    where
        T: Copy,
        ModInt<T>: Mul<ModInt<T>, Output = ModInt<T>>,
    {
        fn mul_assign(&mut self, rhs: ModInt<T>) {
            *self = *self * rhs;
        }
    }

    impl<T> Div<T> for ModInt<T>
    where
        T: Copy
            + Add<Output = T>
            + Sub<Output = T>
            + Div<Output = T>
            + BitAnd<Output = T>
            + PartialEq
            + PartialOrd
            + ShrAssign
            + RemAssign
            + MulAssign,
    {
        type Output = Self;
        fn div(self, mut rhs: T) -> Self::Output {
            if rhs >= self.modulo() {
                rhs %= self.modulo();
            }
            let one = self.modulo() / self.modulo();
            let two = one + one;
            self * Self::new_unchecked(rhs, self.modulo()).pow(self.modulo() - two)
        }
    }
}

fn dfs(v: usize, p: usize, graph: &Vec<Vec<(usize, i64)>>, longest: &mut Vec<i64>) {
    for &(next, cost) in graph[v].iter() {
        if p == next {
            continue;
        }
        longest[next] = max(longest[v], cost);
        dfs(next, v, graph, longest);
    }
}

pub struct UnionFind {
    parent: Vec<usize>,
    sizes: Vec<usize>,
    size: usize,
}

impl UnionFind {
    pub fn new(n: usize) -> UnionFind {
        UnionFind {
            parent: (0..n).map(|i| i).collect::<Vec<usize>>(),
            sizes: vec![1; n],
            size: n,
        }
    }

    pub fn find(&mut self, x: usize) -> usize {
        if x == self.parent[x] {
            x
        } else {
            let px = self.parent[x];
            self.parent[x] = self.find(px);
            self.parent[x]
        }
    }

    pub fn unite(&mut self, x: usize, y: usize) -> bool {
        let parent_x = self.find(x);
        let parent_y = self.find(y);
        if parent_x == parent_y {
            return false;
        }

        let (large, small) = if self.sizes[parent_x] < self.sizes[parent_y] {
            (parent_y, parent_x)
        } else {
            (parent_x, parent_y)
        };

        self.parent[small] = large;
        self.sizes[large] += self.sizes[small];
        self.sizes[small] = 0;
        self.size -= 1;
        true
    }
}

pub struct IO<R, W: std::io::Write>(R, std::io::BufWriter<W>);

impl<R: std::io::Read, W: std::io::Write> IO<R, W> {
    pub fn new(r: R, w: W) -> Self {
        Self(r, std::io::BufWriter::new(w))
    }
    pub fn write<S: ToString>(&mut self, s: S) {
        use std::io::Write;
        self.1.write_all(s.to_string().as_bytes()).unwrap();
    }
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        use std::io::Read;
        let buf = self
            .0
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r' || b == b'\t')
            .take_while(|&b| b != b' ' && b != b'\n' && b != b'\r' && b != b'\t')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }
    pub fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}