Hello people..! This is a special extension for my discussion on **Graph Theory Basics**. Here, I give you the code for implementing the Adjacency List using the C++ STL. Some of the features of this code are –

- The Adjacency List is a vector of list, where each element is a pair, from the utility header file. This pair stores two values, the destination vertex, (V
_{2}in an edge V_{1}→ V_{2}) and the weight of the edge. - For adding an edge, all we have to do is to call push_back() function. Although it does not represent our addEdge() in the initial discussion where we had head insertion, it is tail insertion which is an O(1) insertion operation.
- The vector representing the vertices is 1-indexed.

/* * Adjacency List for * Directed Weighted Graph * Code using C++ STL * * Authored by, * Vamsi Sangam. * */ #include <cstdio> #include <vector> #include <list> #include <utility> using namespace std; int main() { int vertices, edges, v1, v2, weight; printf("Enter the Number of Vertices -\n"); scanf("%d", &vertices); printf("Enter the Number of Edges -\n"); scanf("%d", &edges); // Adjacency List is a vector of list. // Where each element is a pair<int, int> // pair.first -> the edge's destination // pair.second -> edge's weight vector< list< pair<int, int> > > adjacencyList(vertices + 1); printf("Enter the Edges V1 -> V2, of weight W\n"); for (int i = 1; i <= edges; ++i) { scanf("%d%d%d", &v1, &v2, &weight); // Adding Edge to the Directed Graph adjacencyList[v1].push_back(make_pair(v2, weight)); } printf("\nThe Adjacency List-\n"); // Printing Adjacency List for (int i = 1; i < adjacencyList.size(); ++i) { printf("adjacencyList[%d] ", i); list< pair<int, int> >::iterator itr = adjacencyList[i].begin(); while (itr != adjacencyList[i].end()) { printf(" -> %d(%d)", (*itr).first, (*itr).second); ++itr; } printf("\n"); } return 0; }

Feel free to comment if you have any doubts..! **Commenting is super easy if you are a Facebook, Twitter or a Google+ user**…! So, don’t hesitate..! 😉 … Keep practising..! Happy Coding..! 😀

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I got it, because it’s in scanf the C way. sorry I got confused, I usually use cin/cout

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Everybody gets confused… 😉 … I am more used to printf() and scanf()… Let me know if you have any more doubts…! 😀

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Why did you use references when calling to input edges and vertices?

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