UVA 10986 - Sending email

这道题就是在求最短路，而且是单源最短路吗，所以我先想到了dijkstra算法，结果TLE了，

dijkstra的代码：

#include<stdio.h>
#include<string.h>
#define INF 200000005
#define MAXD 20005
int u, v, w, S, T, n, m, N;
int d[MAXD][MAXD], f[MAXD];
bool vis[MAXD];

int min( int a, int b)
{
    return a < b ? a : b;
}

void init()
{
    for( int i = 0; i < n; i ++)
        f[i] = ( i == S ? 0 : INF );
    memset( vis, false, sizeof vis);
    for( int i = 0; i < n; i ++)
        for( int j = 0; j < n; j ++)
        {
            if( i == j) d[i][j] = 0;
            else d[i][j] = INF;
        }
    for( int i = 0; i < m; i ++)
    {
        scanf( "%d%d%d", &u, &v, &w);
        d[u][v] = d[v][u] = w;
    }
}

void dijkstra()
{
    for( int i = 0; i < n; i ++)
    {
        int x, tt = INF;
        for( int y = 0; y < n; y ++)
            if( !vis[y] && f[y] <= tt)
                tt = f[ x = y];
        vis[x] = true;
        for( int y = 0; y < n; y ++) {
            f[y] = min( f[y], f[x] + d[x][y]);
        }
    }
}

int main()
{
    scanf( "%d", &N);
    for( int cas = 1; cas <= N; cas ++)
    {
        scanf( "%d%d%d%d", &n, &m, &S, &T);
        init();
        dijkstra();
        if( f[T] >= INF) printf( "Case #%d: unreachable\n", cas);
        else
            printf( "Case #%d: %d\n", cas, f[T]);
    }
    return 0;
}

下面参考了staginner的SPFA：

#include<stdio.h>
#include<string.h>
#define MAXD 100005
#define INF 200000005

int N, n, m, S, T, e, a, b, c, cas;
int first[MAXD], next[MAXD], v[MAXD], w[MAXD], d[MAXD], q[MAXD];
bool inq[MAXD];

void input( int a, int b, int c)
{
    v[e] = b;
    w[e] = c;
    next[e] = first[a];
    first[a] = e;
    e ++;
}

void init()
{
    scanf( "%d%d%d%d", &n, &m, &S, &T);
    memset( first, -1, sizeof first);
    e = 0;
    for( int i = 0; i < m; i ++)
    {
        scanf( "%d%d%d", &a, &b, &c);
        input( a, b, c);
        input( b, a, c);
    }
}

void SPFA()
{
    int front, rear, u;
    front = rear = 0;
    for( int i = 0; i < n; i ++)
        d[i] = ( i == S ? 0 : INF);
    q[rear ++] = S;
    while( front != rear)
    {
        u = q[front ++];
        if( front == n) front = 0;
        inq[u] = false;
        for( int i = first[u]; i != -1; i = next[i])
            if( d[u] + w[i] < d[v[i]])
            {
                d[ v[i] ] = d[u] + w[i];
                if( !inq[ v[i] ])
                {
                    q[rear ++] = v[i];
                    if( rear == n) rear = 0;
                    inq[ v[i]] = true;
                }
            }
    }
    if( d[T] == INF)
        printf( "Case #%d: unreachable\n", cas);
    else
        printf( "Case #%d: %d\n", cas, d[T]);
}

int main()
{
    scanf( "%d", &N);
    for( cas = 1; cas <= N; cas ++)
    {
        init();
        SPFA();
    }
    return 0;
}