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/* | |
Ways to Represent Graphs | |
Charles (@c650) | |
Showing how to represent _unweighted_ graphs | |
in C++. | |
*/ | |
#include <iostream> | |
#include <vector> | |
struct edge { | |
int a,b; | |
}; | |
int main(void) { | |
/* the number of nodes, n*/ | |
int n; | |
std::cin >> n; | |
/* number of edges, m*/ | |
int m; | |
std::cin >> m; | |
/* imagine we are taking in some number n edges represented as node pairs a,b*/ | |
/* | |
Here's an adjacency matrix, a vector of N vectors of N bools. | |
adjacency_matrix[i][j] is true if there is an edge directly between nodes i and j. | |
If the graph is _undirected_ adjacency_matrix[i][j] and adjacency_matrix[j][i] | |
must have the same value. | |
*/ | |
std::vector<std::vector<bool>> adjacency_matrix(n, std::vector<bool>(n, false)); | |
/* | |
This is our adjacency list, a vector of N vectors. | |
But each element of the list (e.g., adjacency_list[i]) | |
is an _empty_ vector. | |
*/ | |
std::vector<std::vector<int>> adjacency_list(n); | |
/* | |
A vector of edges. Useful in some cases when you care | |
more about the edges than the nodes they connect. | |
*/ | |
std::vector<edge> edges(m); | |
int a,b; /* variables for our edge pairs (input of a and b should be in [0,n) */ | |
/* read in `m` edges */ | |
for (int i = 0; i < m; ++i) { | |
std::cin >> a >> b; | |
/* what always happens */ | |
adjacency_matrix[a][b] = true; | |
adjacency_list[a].push_back(b); | |
/* ONLY do this part if the graph is undirected. */ | |
adjacency_matrix[b][a] = true; | |
adjacency_list[b].push_back(a); | |
/* also store the edge */ | |
edges[i] = { a , b }; | |
} | |
return 0; | |
} |
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std::bad_alloc called when initializing a graph G(8,8)