Add Longest Flight Route.cpp for finding the longest path in a directed graph

Author: Tamim-saad

Longest Flight Route.cpp

@@ -0,0 +1,73 @@
+// say Alhamdulillah
+
+#include <algorithm>
+#include <bits/stdc++.h>
+using namespace std;
+#define ll long long
+#define eb emplace_back
+
+#define forr(i, a, b) for (ll i = a; i < b; i++)
+#define fast                                                                   \
+  ios_base::sync_with_stdio(0);                                                \
+  cin.tie(0);                                                                  \
+  cout.tie(0);
+
+vector<vector<ll>> adj_list;
+vector<ll> vis, topoPath;
+
+void dfs(ll curr) {
+  vis[curr] = 1;
+  
+  for (ll neigh : adj_list[curr]) {
+    if (!vis[neigh]) {
+      dfs(neigh);
+    }
+  }
+  topoPath.emplace_back(curr);
+}
+
+int main() {
+  fast;
+  ll n, m, x, y, i;
+  cin >> n >> m;
+
+  vector<ll> par(n + 1), dist(n + 1), ans;
+  adj_list.resize(n + 1);
+  vis.resize(n + 1, 0);
+
+  for (i = 1; i <= m; i++) {
+    cin >> x >> y;
+    adj_list[x].emplace_back(y);
+  }
+
+  dfs(1);
+
+  if (vis[n] == 0) {
+    cout << "IMPOSSIBLE\n";
+    return 0;
+  }
+
+  reverse(topoPath.begin(),topoPath.end());
+
+  for (auto i : topoPath) {
+    for (auto x : adj_list[i]) {
+      if (dist[i] + 1 > dist[x]) {
+        dist[x] = dist[i] + 1;
+        par[x] = i;
+      }
+    }
+  }
+
+  x = n;
+  while (x != 0) {
+    ans.eb(x);
+    x = par[x];
+  }
+
+  reverse(ans.begin(), ans.end());
+  cout << ans.size() << endl;
+
+  for (auto x : ans) {
+    cout << x << " ";
+  }
+}