Add euler path in graph

Author: YazanRi

Graph/EulerPath/euler_path.cpp

@@ -0,0 +1,35 @@
+// O(V + E)
+// Euler path is a path that uses every edge in graph exactly once
+// const int N = 1e5 + 50;
+int n, in[N], out[N]; // in and out degrees
+vector<int> path;  // has the euler path in reverse order
+queue<int> adj[N];
+
+void dfs(int u)
+{
+    while(adj[u].size())
+    {
+        int v = adj[u].front();
+        adj[u].pop();
+        dfs(v);
+    }
+    path.push_back(u);
+}
+
+pair<bool, int> is_eulerian() // {is eulerian, start node of dfs}
+{
+    int _s = 0, _e = 0, st = 1;
+    for(int u = 1; u < N; u++)
+    {
+        int sub = in[u] - out[u];
+        if(sub == -1)
+            ++_s, st = u;
+        else if(sub == 1)
+            ++_e;
+        else if(sub != 0)
+            return {0, -1};
+    }
+    if(_s > 1 || _e > 1 || _s + _e == 1)
+        return {0, -1};
+    return {1, st};
+}