# Graph implementation using STL for competitive programming | Set 2 (Weighted graph)

In Set 1, unweighted graph is discussed. In this post, weighted graph representation using STL is discussed. The implementation is for adjacency list representation of weighted graph.

We use two STL containers to represent graph:

- vector : A sequence container. Here we use it to store adjacency lists of all vertices. We use vertex number as index in this vector.
- pair : A simple container to store pair of elements. Here we use it to store adjacent vertex number and weight of edge connecting to the adjacent.

The idea is to use a vector of pair vectors. Below code implements the same.

`// C++ program to represent undirected and weighted graph ` `// using STL. The program basically prints adjacency list ` `// representation of graph ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// To add an edge ` `void` `addEdge(vector <pair<` `int` `, ` `int` `> > adj[], ` `int` `u, ` ` ` `int` `v, ` `int` `wt) ` `{ ` ` ` `adj[u].push_back(make_pair(v, wt)); ` ` ` `adj[v].push_back(make_pair(u, wt)); ` `} ` ` ` `// Print adjacency list representaion ot graph ` `void` `printGraph(vector<pair<` `int` `,` `int` `> > adj[], ` `int` `V) ` `{ ` ` ` `int` `v, w; ` ` ` `for` `(` `int` `u = 0; u < V; u++) ` ` ` `{ ` ` ` `cout << ` `"Node "` `<< u << ` `" makes an edge with \n"` `; ` ` ` `for` `(` `auto` `it = adj[u].begin(); it!=adj[u].end(); it++) ` ` ` `{ ` ` ` `v = it->first; ` ` ` `w = it->second; ` ` ` `cout << ` `"\tNode "` `<< v << ` `" with edge weight ="` ` ` `<< w << ` `"\n"` `; ` ` ` `} ` ` ` `cout << ` `"\n"` `; ` ` ` `} ` `} ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` `int` `V = 5; ` ` ` `vector<pair<` `int` `, ` `int` `> > adj[V]; ` ` ` `addEdge(adj, 0, 1, 10); ` ` ` `addEdge(adj, 0, 4, 20); ` ` ` `addEdge(adj, 1, 2, 30); ` ` ` `addEdge(adj, 1, 3, 40); ` ` ` `addEdge(adj, 1, 4, 50); ` ` ` `addEdge(adj, 2, 3, 60); ` ` ` `addEdge(adj, 3, 4, 70); ` ` ` `printGraph(adj, V); ` ` ` `return` `0; ` `} ` |

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Output:

Node 0 makes an edge with Node 1 with edge weight =10 Node 4 with edge weight =20 Node 1 makes an edge with Node 0 with edge weight =10 Node 2 with edge weight =30 Node 3 with edge weight =40 Node 4 with edge weight =50 Node 2 makes an edge with Node 1 with edge weight =30 Node 3 with edge weight =60 Node 3 makes an edge with Node 1 with edge weight =40 Node 2 with edge weight =60 Node 4 with edge weight =70 Node 4 makes an edge with Node 0 with edge weight =20 Node 1 with edge weight =50 Node 3 with edge weight =70

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