Merge pull request #26 from coolsks/patch-4

IsGraphATree.cpp

Author: sunnyshahabuddin

IsGraphATree.cpp

@@ -0,0 +1,81 @@
+
+//Is the given graph a tree ?
+// Two conditions
+//1. Should not contain a cycle : no of edges = n-1
+//2. 1 connected component
+
+#include <bits/stdc++.h>
+using namespace std;
+
+#define ll long long
+#define pb push_back
+#define mp make_pair
+#define ff first
+#define ss second
+#define f(i, a, n) for (i = a; i < n; i++)
+#define fe(i, a, n) for (i = a; i <= n; i++)
+#define w(x)  \
+	int x;    \
+	cin >> x; \
+	while (x--)
+#define mod 1000000007
+#define ps(x, y) fixed << setprecision(y) << x
+
+void sks()
+{
+#ifndef ONLINE_JUDGE
+	freopen("input.txt", "r", stdin);
+	freopen("output.txt", "w", stdout);
+#endif
+
+	ios_base::sync_with_stdio(false);
+	cin.tie(NULL);
+	cout.tie(NULL);
+}
+
+vector<int> adj[10001];
+int vis[10001];
+
+void dfs(int node)
+{
+	vis[node] = 1;
+
+	for (int child : adj[node])
+	{
+		if (!vis[child])
+			dfs(child);
+	}
+}
+
+int main()
+{
+	sks();
+
+	int n, m, a, b, i, cv = 0;
+	cin >> n >> m;
+
+	fe(i, 1, m)
+	{
+		cin >> a >> b;
+		adj[a].pb(b);
+		adj[b].pb(a);
+	}
+
+	cv = 0;
+	fe(i, 1, n)
+	{
+		if (vis[i] == 0)
+		{
+			dfs(i);
+			cv++;
+		}
+	}
+
+	if (cv == 1 && m == n - 1)
+		cout << "YES" << endl;
+
+	else
+		cout << "NO" << endl;
+
+	return 0;
+}