UVa 10986 - Sending email

SPFA，2RE，无向图的边数为题目描述的两倍。

# include <cstdio>

# include <cstring>

# include <queue>



using namespace std;



# define N 20000 + 5

# define M (50000 + 5) * 2

# define INF 550000000



int n, m, src, des;



int first[N], d[N];

bool inq[N];

int u[M], v[M], w[M], next[M];



void read_graph(void)

{

    scanf("%d%d%d%d", &n, &m, &src, &des);

    memset(first, -1, sizeof(first[0])*n);

    for (int e = 0; e < 2*m; e += 2)

    {

        scanf("%d%d%d", &u[e], &v[e], &w[e]);

        next[e] = first[u[e]], first[u[e]] = e;

        u[e+1] = v[e], v[e+1] = u[e], w[e+1] = w[e];

        next[e+1] = first[u[e+1]], first[u[e+1]] = e+1;

    }

}



void spfa(int src, int n)

{

    queue <int> Q;

    

    memset(inq, false, sizeof(inq[0])*n);

    for (int i = 0; i < n; ++i) d[i] = (i==src ? 0:INF);

    Q.push(src);

    while (!Q.empty())

    {

        int x = Q.front(); Q.pop(); inq[x] = false;

        for (int e = first[x]; e != -1; e = next[e]) if (d[x] < INF && d[x]+w[e] < d[v[e]])

        {

            d[v[e]] = d[x] + w[e];

            if (inq[v[e]] == false)

            {

                inq[v[e]] = true;

                Q.push(v[e]);

            }

        }

    }

}



int main()

{

    int T;

        

    scanf("%d", &T);

    for (int i = 1; i <= T; ++i)

    {

        printf("Case #%d:", i);

        read_graph();

        spfa(src, n);

        if (d[des] >= INF) puts(" unreachable");

        else printf(" %d\n", d[des]);

    }

    

    return 0;

}