60 lines
1.4 KiB
C++
60 lines
1.4 KiB
C++
// Algorithm outputting a topological order of a directed graph
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// Authors: Georǵi Kocharyan
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#include <iostream>
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#include <cstdio>
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#include <vector>
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#include <stack>
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#include "../digraph.h"
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int main() {
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int size = 10;
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Digraph G(size);
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G.add_edge(3,4);
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// G.add_edge(4,3);
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// G.add_edge(5,6);
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G.add_edge(6,7);
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G.add_edge(7,5);
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// G.add_edge(7,3);
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// G.add_edge(0,3);
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// G.add_edge(3,0);
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// keeps track of vertices with zero indegree, these can be put at the beginning
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std::stack<int> zero_indegree;
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std::vector<int> indegs = G.indegrees();
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int amount = 0;
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for(int i = 0; i < size; i++)
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{
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if (indegs[i] == 0)
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{
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zero_indegree.push(i);
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amount++;
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}
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}
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// update indegs, zero_indegree after adding a vertex to the top. order
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while(!zero_indegree.empty())
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{
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int node_id = zero_indegree.top();
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zero_indegree.pop();
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std::cout << node_id << ' ';
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for(auto i: G.adjList(node_id))
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{
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if (indegs[i] = 1) // this ensures each vertex added to stack only once
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{
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zero_indegree.push(i);
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amount++;
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}
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indegs[i]--;
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}
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}
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if (!(amount == size))
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{
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std::cout << '\n' << "The graph contains cycles and thus has no topological order." << std::endl;
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}
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return 0;
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} |