Shortest Path in a Graph

Lab C++ Advanced 30 points

Read an undirected graph (n nodes 1..n, m edges) and two nodes s, t. Print the number of edges on the shortest path, or -1, using BFS on an adjacency list.

Input

n m, m lines u v, then s t.

Output

One integer.

Example

Input

Output

Sample input available Sample output available

Editor

C++

Hints

BFS explores nodes in order of distance from s.

Solution explanation

An adjacency list (vector of vectors) is the usual way to store sparse graphs.

Show solution

#include <iostream>
#include <queue>
#include <vector>
using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector<vector<int>> adj(n + 1);
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    int s, t;
    cin >> s >> t;
    vector<int> dist(n + 1, -1);
    queue<int> q;
    dist[s] = 0;
    q.push(s);
    while (!q.empty()) {
        int u = q.front();
        q.pop();
        for (int v : adj[u]) {
            if (dist[v] == -1) {
                dist[v] = dist[u] + 1;
                q.push(v);
            }
        }
    }
    cout << dist[t] << "\n";
    return 0;
}

Output

Answer