Question

我必须为有向图实现一个类，我需要检索与边相关的成本以及在O（1）中插入/更改成本。使用std :: map很好，唯一的问题是它对于指定的需求平均需要O（logn），所以我看了一眼std :: unordered_map并尝试在我的程序中使用它。唯一的问题是我不太了解编译错误。

这些是我尝试访问unordered_map的行（试过[]以及.insert或.find，仍然不起作用）

void DirectedGraph::setValueOfMapEdge(int node1, int node2, int cost) {
        mapEdges.insert({{node1, node2}, cost});
    }

int DirectedGraph::getValueOfMapEdge(int node1, int node2) {
        return mapEdges[make_pair(node1, node2)];
    }

这是错误日志https://hastebin.com/qawamosuso.vbs

这是完整的代码（抱歉缺少评论）

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <unordered_map>
using namespace std;

class DirectedGraph {
public:
    DirectedGraph() {
        noVertices = 0;
        outboundEdges = inboundEdges = vector<vector<int>>();
    }
    void readFromFile(string fileName);
    void setNoVertices(int vertices);
    void addEdge(int node1, int node2);
    void setValueOfMapEdge(int node1, int node2, int cost);
    int getValueOfMapEdge(int node1, int node2);
    void resizeGraph(int noVertices);
    bool isEdgeBetweenNodes(int node1, int node2);
    int getInDegree(int node);
    int getOutDegree(int node);
    int getNoVertices();
    vector<int> getOutboundNeighboursVector(int node);
    vector<int> getInboundNeighboursVector(int node);
    friend class VertexIterator;

private:
    int noVertices;
    vector<vector<int>> outboundEdges;
    vector<vector<int>> inboundEdges;
    unordered_map<pair<int,int>, int> mapEdges;
    vector<int> inDegree, outDegree;
};

class VertexOutboundIterator {
public:
    VertexOutboundIterator(DirectedGraph *directedGraph, int node) {
        graph = directedGraph;
        vertex = node;
    }
    void first();
    void next();
    bool isDone();
    int currentItem();

private:
    DirectedGraph *graph;
    int vertex;
    int index;
};

void VertexOutboundIterator::first() {
    index = 0;
}

void VertexOutboundIterator::next() {
    ++index;
}

bool VertexOutboundIterator::isDone() {
    return index == graph->getOutboundNeighboursVector(vertex).size();
}

int VertexOutboundIterator::currentItem() {
    return graph->getOutboundNeighboursVector(vertex)[index];
}

class VertexInboundIterator {
public:
    VertexInboundIterator(DirectedGraph *directedGraph, int node) {
        graph = directedGraph;
        vertex = node;
    }

    void first();

    void next();

    bool isDone();

    int currentItem();

private:
    DirectedGraph *graph;
    int vertex;
    int index;
};

void VertexInboundIterator::first() {
    index = 0;
}

void VertexInboundIterator::next() {
    ++index;
}

bool VertexInboundIterator::isDone() {
    return index == graph->getInboundNeighboursVector(vertex).size();
}

int VertexInboundIterator::currentItem() {
    return graph->getInboundNeighboursVector(vertex)[index];
}


vector<int> DirectedGraph::getInboundNeighboursVector(int node) {
    return inboundEdges[node];
}

vector<int> DirectedGraph::getOutboundNeighboursVector(int node) {
    return outboundEdges[node];
}

void DirectedGraph::readFromFile(string fileName) {
    ifstream fin(fileName);
    int noVertices = 0, noEdges = 0;
    fin >> noVertices >> noEdges;
    setNoVertices(noVertices);
    resizeGraph(noVertices);
    int x, y, c;
    for ( int i = 0; i < noEdges; ++i ) {
        fin >> x >> y >> c;
        DirectedGraph::addEdge(x,y);
        DirectedGraph::setValueOfMapEdge(x,y,c);
    }
}

void DirectedGraph::setNoVertices(int vertices) {
    noVertices = vertices;
}

void DirectedGraph::resizeGraph(int noVertices) {
    outboundEdges = inboundEdges = vector<vector<int>>(noVertices);
    inDegree = outDegree = vector<int>(noVertices);
}

void DirectedGraph::addEdge(int node1, int node2) {
    outboundEdges[node1].push_back(node2);
    inboundEdges[node2].push_back(node1);
    inDegree[node2]++;
    outDegree[node1]++;
}

void DirectedGraph::setValueOfMapEdge(int node1, int node2, int cost) {
    mapEdges.insert({{node1, node2}, cost});
}

int DirectedGraph::getValueOfMapEdge(int node1, int node2) {
    return mapEdges[make_pair(node1, node2)];
}

int DirectedGraph::getNoVertices() {
    return noVertices;
};

bool DirectedGraph::isEdgeBetweenNodes(int node1, int node2) {
    for ( const auto node : outboundEdges[node1] )
        if (node == node2)
            return true;
    return false;
}

int DirectedGraph::getInDegree(int node) {
    return inDegree[node];
}

int DirectedGraph::getOutDegree(int node) {
    return outDegree[node];
}

int main() {
    DirectedGraph g = DirectedGraph();
    g.readFromFile("1.txt");
    /*cout << g.isEdgeBetweenNodes(2,0) << '\n';
    cout << g.getOutDegree(2) << '\n';

    VertexOutboundIterator vt = VertexOutboundIterator(&g, 2);
    for ( vt.first(); !vt.isDone(); vt.next() ) {
        cout << vt.currentItem() << '\n';
    }

    VertexInboundIterator ivt = VertexInboundIterator(&g, 3);
    for ( ivt.first(); !ivt.isDone(); ivt.next() )
        cout << ivt.currentItem() << '\n'; */

    cout << g.getValueOfMapEdge(0, 1);

    return 0;
}

我正在使用g ++，该版本支持c ++ 11。任何想法都会非常感激。

Answer 1

您使用std::pair作为密钥。对于std::unordered_map，需要使用std::hash对密钥进行哈希处理，std::pair没有专门化。

虽然Boost hash library有它，除非你想自己做这样的专业化。

STL unordered_map编译错误

1 个答案: