Standard input output usage

Taking fast input output

In some of the problems in SDE 1 and SDE 2 online coding rounds, you have to take care of the program inputs. Use this following two lines of code to increase your i/o speed in competitive programming contests.

Brief explanation:

• If you include ios::sync_with_stdio(false), then mixing C (scanf, printf) and C++ (cin, cout) style I/O may produce unexpected results. The upside is that both cin / cout become faster.
• Including cin.tie(nullptr) will reduce the runtime if you are interleaving cin and cout (as is the case in the task at hand).

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    /* code */

    return 0;
}

Taking data in and writing data out to a file

Here is an example of how we can write all inputs to a text file and then run our algorithms.

You must add 2 files called input.txt and output.txt in the same directory add the function in the code, then in the main() function just call the function fileIO() to have the input taken from input.txt and the output written to output.txt.

void fileIO() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
}

int main() {

    fileIO();

    // ... YOUR CODE ...
    return 0;
}

Input

Now in the input.txt file, you design as the inputs are given in the following case the input was

3
a
b
c
4
a b 12
c b 2
b a 99
c a 8

Output

The corresponding output file is written as

c [a: 8][b: 2]
b [a: 99]
a [b: 12]

a->b
c->b
b->a
c->a

Code

#include <iostream>
#include <list>
#include <unordered_map>
#include <vector>
#include <utility>

using namespace std;

// Directed graph implementation
class Graph{
private:
    unordered_map<char, list<pair<char, int>>> adj_list;
    vector<pair<char, char>> E; // edge set
public:
    vector<pair<char, char>> edges(){
        return E;
    }

    void add_edge(char vertex1, char vertex2, int weight){
        adj_list[vertex1].push_front(make_pair(
            vertex2, weight
        ));

        E.push_back({vertex1, vertex2});
    }

    void register_vertex(vector<char> vertices){
        for (auto v:vertices){
            list<pair<char, int>> l;
            adj_list.insert({v, l});
        }
    }

    unordered_map<char, list<pair<char, int>>> view(){
        return adj_list;
    }
};


int main() {

    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    Graph g;

    int vertex;
    cin >> vertex;

    vector<char> v;

    while (vertex != 0){
        char vertex_label;
        cin >> vertex_label;
        v.push_back(vertex_label);
        vertex--;
    }

    g.register_vertex(v);

    int numberofedges;

    cin >> numberofedges;

    while(numberofedges != 0){
        char from, to;
        int weight;

        cin >> from >> to >> weight;
        g.add_edge(from, to, weight);
        numberofedges--;
    }

    unordered_map<char, list<pair<char, int>>> map = g.view();

    for (auto data:map){
        cout << data.first << " ";

        for (auto neighbor:data.second)
            cout << "[" << neighbor.first << ": " << neighbor.second << "]";

        cout << "\n";
    }

    cout << "\n";

    // print all the edges
    auto edges = g.edges();
    for (auto edge:edges){
        cout << edge.first << "->" << edge.second << "\n";
    }

    cout << "\n";
}

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