Added Kruskal's MST Algorithm

Author: avishkarhande

Graph/Kruskal_Minimum_Spanning_Using_Disjoint_Set.cpp

@@ -0,0 +1,69 @@
+// Author : Avishkar A. Hande
+
+#include<bits/stdc++.h>
+#define ll long long
+using namespace std;
+
+const int maxS = 1e5+10;
+vector<pair<ll, ll>> adj[maxS];
+
+template <typename T>
+class DisjointSet{
+public:
+    vector<T> parent;
+    DisjointSet(T n){
+        parent.resize(n+1);
+        for(T i = 0; i <= n; i++) parent[i] = i;
+    }
+    T find(T a){
+        if(parent[a] == a) return a;
+        return parent[a] = find(parent[a]);
+    }
+    void join(T a, T b){
+        if(find(a) == find(b)) return;
+        parent[find(a)] = find(b);
+        return ;
+    }
+};
+
+
+// this function stores the MST in adjacency list
+// Note : It does not store the original graph
+
+void kruskal(ll n, vector<vector<ll>> &edges){
+    sort(edges.begin(), edges.end());
+    DisjointSet<ll> d(n+1);
+    for(int i = 0; i < edges.size(); i++){
+        if(d.find(edges[i][1])!=d.find(edges[i][2])){
+            d.join(d.find(edges[i][1]), d.find(edges[i][2]));
+            adj[edges[i][1]].push_back({edges[i][2],edges[i][0]});
+            adj[edges[i][2]].push_back({edges[i][1],edges[i][0]});
+        }
+    }
+}
+
+int main()
+{
+    #ifndef ONLINE_JUDGE
+        freopen("input.txt", "r", stdin);
+        freopen("output.txt", "w", stdout);
+    #endif
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+    ll nodes, edges;
+    cin >> nodes >> edges;
+    vector<vector<ll>> edgesv;
+    for(int i = 0; i < edges; i++){
+        ll v1, v2, w;
+        cin >> v1 >> v2 >> w;
+        edgesv.push_back({w, v1, v2});
+    }
+    kruskal(nodes, edgesv);
+    for(int i = 1; i <= nodes; i++){
+        for(pair<ll, ll> p : adj[i]){
+            cout << i << " " << p.first << " " << p.second << endl;
+        }
+    }
+}
+
+