BFS Traversal Problem

CP/GST January SRM/problem3.cpp

@@ -0,0 +1,66 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <queue>
+#include <cassert>
+
+using namespace std;
+
+void solve() {
+  int n, m, s, e;
+  cin >> n >> m >> s >> e;
+
+  assert(1 <= n);
+  assert(1 <= m);
+  assert(1 <= s && s <= n);
+  assert(1 <= e && e <= n);
+
+  s--;
+  e--;
+
+  vector<int> dist(n, -1);
+
+  vector<vector<int>> g(n);
+  for (int i = 0; i < m; i++) {
+    int u, v;
+    cin >> u >> v;
+    assert(1 <= u && u <= n);
+    assert(1 <= v && v <= n);
+    u--;
+    v--;
+    g[u].push_back(v);
+    g[v].push_back(u);
+  }
+
+  queue<int> q;
+  q.push(s);
+  dist[s] = 0;
+
+  while (!q.empty()) {
+    int u = q.front(); q.pop();
+    for (int v : g[u]) {
+      if (dist[v] == -1) {
+        dist[v] = dist[u] + 1;
+        q.push(v);
+      }
+    }
+  }
+
+  if (s == e) {
+    printf("NO\n");
+  } else if (dist[e] == -1) {
+    printf("NO\n");
+  } else {
+    printf("YES %d\n", max(0, dist[e] - 1));
+  }
+}
+
+int main() {
+  int t;
+  cin >> t;
+  assert(1 <= t);
+
+  while (t--) {
+    solve();
+  }
+}