graph/transpose_graph.hpp

• View this file on GitHub
• Last update: 2021-08-30 04:35:37+09:00
• Include: #include "graph/transpose_graph.hpp"
• Link: https://en.wikipedia.org/wiki/Transpose_graph

Depends on

• utils/macros.hpp

Required by

• graph/quotient_graph.hpp
• strongly connected components decomposition, Kosaraju's algorithm / 強連結成分分解 (graph/strongly_connected_components.hpp)
• 2-SAT ($O(N)$) (utils/two_satisfiability.hpp)

Verified with

• graph/strongly_connected_components.yosupo.test.cpp
• utils/two_satisfiability.yosupo.test.cpp

Code

#pragma once
#include <vector>
#include "../utils/macros.hpp"

/**
 * @param g is an adjacent list of a digraph
 * @note $O(V + E)$
 * @see https://en.wikipedia.org/wiki/Transpose_graph
 */
std::vector<std::vector<int> > make_transpose_graph(std::vector<std::vector<int> > const & g) {
    int n = g.size();
    std::vector<std::vector<int> > h(n);
    REP (i, n) {
        for (int j : g[i]) {
            h[j].push_back(i);
        }
    }
    return h;
}

#line 2 "graph/transpose_graph.hpp"
#include <vector>
#line 2 "utils/macros.hpp"
#define REP(i, n) for (int i = 0; (i) < (int)(n); ++ (i))
#define REP3(i, m, n) for (int i = (m); (i) < (int)(n); ++ (i))
#define REP_R(i, n) for (int i = (int)(n) - 1; (i) >= 0; -- (i))
#define REP3R(i, m, n) for (int i = (int)(n) - 1; (i) >= (int)(m); -- (i))
#define ALL(x) std::begin(x), std::end(x)
#line 4 "graph/transpose_graph.hpp"

/**
 * @param g is an adjacent list of a digraph
 * @note $O(V + E)$
 * @see https://en.wikipedia.org/wiki/Transpose_graph
 */
std::vector<std::vector<int> > make_transpose_graph(std::vector<std::vector<int> > const & g) {
    int n = g.size();
    std::vector<std::vector<int> > h(n);
    REP (i, n) {
        for (int j : g[i]) {
            h[j].push_back(i);
        }
    }
    return h;
}

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