03-algorithms_on_graphs/01-decomposition/01-reachability/reachability.cpp


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#include <iostream>
#include <vector>
#include <stack>

using std::vector;
using std::stack;
using std::pair;


int reach(vector<vector<int> > &adj, int x, int y)
{
    vector<bool> visited(adj.size());
    stack<int> st;

    st.push(x);

    while(!st.empty()) {
        int v = st.top();
        if (v == y)
            return 1;
        st.pop();
        visited[v] = true;
        int s = adj[v].size();
        for (int i = 0; i < s; i++) {
            int w = adj[v][i];
            if (!visited[w])
                st.push(w);
        }
    }

    return 0;
}

int main() {
  size_t n, m;
  std::cin >> n >> m;
  vector<vector<int> > adj(n, vector<int>());
  for (size_t i = 0; i < m; i++) {
    int x, y;
    std::cin >> x >> y;
    adj[x - 1].push_back(y - 1);
    adj[y - 1].push_back(x - 1);
  }
  int x, y;
  std::cin >> x >> y;
  std::cout << reach(adj, x - 1, y - 1) << '\n';
}