Implementation：Bellman-ford

单源最短路径算法Bellman-ford练习，可以处理有负边的情况（也可以在存在负圈时及时终止）

#include <iostream>

#include <cstdlib>

#include <vector>



using namespace std;



class Edge {

public:

    int from;

    int to;

    int cost;

};



int main() {

    

    int graph[5][5] =   {

                            0, 1, 5, 0, 0,

                            0, 0, 3,10, 9,

                            0, 0, 0, 5, 0,

                            0, 1, 0, 0, 1,

                            0, 0, 0, 0, 0,

                        };

    Edge edge;



    vector<Edge> E;

    vector<int>  vd(5, INT_MAX);

    for (int i=0; i<5; i++) {

        for (int j=0; j<5; j++) {

            edge.cost = graph[i][j];

            if (edge.cost == 0) continue;

            edge.to  = j;

            edge.from= i;

            E.push_back(edge);

        }

    }

    

    vd[0] = 0; // start point



    bool update = true;

    while (update) {

        update = false;

        for (int i=0; i<E.size(); i++) {

            Edge& e = E[i];

            if (vd[e.from] != INT_MAX && vd[e.to] > vd[e.from] + e.cost) {

                update = true;

                vd[e.to] = vd[e.from] + e.cost;

            }

        }

    }



    for (int i=0; i<5; i++)

        cout<<i<<":"<<vd[i]<<endl;

    system("pause");

    return 0;

}