Update main.cpp

11-2/main.cpp

@@ -5,3 +5,86 @@
 Вывод: количество кратчайших путей от v к w.
 
 ссылка на Яндекс.Контест https://contest.yandex.ru/contest/15957/run-report/27592154/
+
+#include <iostream>
+#include <algorithm>
+#include <queue>
+#include <unordered_map>
+#include <assert.h>
+#include <list>
+#include <vector>
+#define INT_MAX 2147483647
+
+using std::list;
+using std::vector;
+using std::queue;
+using std::cout;
+
+class Graph {
+public:
+    Graph(int v): v(v) { adj.assign(v, {}); };
+    void BFS( int src, vector<int>& dist, vector<int>& paths, int n ) const;
+    int find_shortest_paths( int s, int n, int w ) const;
+    void add_edge( int u, int v );
+private:
+    const int v;
+    vector<vector <int> > adj;
+};
+
+void Graph::BFS( int src, vector<int>& dist, vector<int>& paths, int n ) const {
+    vector<bool> visited( n, false );
+    dist[src] = 0;
+    paths[src] = 1;
+
+    queue <int> q;
+    q.push(src);
+    visited[src] = true;
+    while (!q.empty()) {
+        int curr = q.front();
+        q.pop();
+
+        for (auto x : adj[curr]) {
+            if (visited[x] == false) {
+                q.push(x);
+                visited[x] = true;
+            }
+            if (dist[x] > dist[curr] + 1) {
+                dist[x] = dist[curr] + 1;
+                paths[x] = paths[curr];
+            }
+            else if (dist[x] == dist[curr] + 1)
+                paths[x] += paths[curr];
+        }
+    }
+}
+
+int Graph::find_shortest_paths( int s, int n, int w ) const {
+    vector<int> dist( n, INT_MAX );
+    vector<int> paths( n, 0 );
+    BFS( s, dist, paths, n );
+    int result = paths[w];
+    return result;
+}
+
+void Graph::add_edge( int u, int v ) {
+    adj[u].push_back(v);
+    adj[v].push_back(u);
+}
+
+int main() {
+    int v_, n;
+    std::cin >> v_ >> n;
+    Graph g(v_);
+    for ( int i = 0; i < n; ++i ) {
+        int u, v;
+        std::cin >> u >> v;
+        g.add_edge( u, v );
+    }
+    int v, w;
+    std::cin >> v >> w;
+    int result = g.find_shortest_paths( v, v_, w );
+      cout << result << std::endl;
+
+    return 0;
+}
+