poj 1511 Invitation Cards

 

大意：求最短路径

思路：逆向思考，建一次反向图。

今天实现了下Dijkstra + heap，spfa+邻接表大概要2030ms左右，而Dijkstra + heap要2350左右。

还有以后如果题目给出了最大的数据的话最好别用0xfffffff等，直接用它给定的，这里我WA了好多次。

 

CODE：

 

 

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;

const int MAXN = 1000010;
const int MAXM = 1000010;
const int INF = 1000000010;      //特别要注意

int n, m, cnt;
int first[MAXN];
__int64 d[MAXN];
__int64 w[MAXM];
int u[MAXM], v[MAXM], next[MAXM];
int su[MAXM], sv[MAXM];
__int64 sw[MAXM];

void init()
{
    cnt = 0;
    memset(u, 0, sizeof(u));
    memset(v, 0, sizeof(v));
    memset(w, INF, sizeof(w));
    memset(next, 0, sizeof(next));
    memset(d, 0, sizeof(d));
    memset(first, -1, sizeof(first));
}

void read_graph(int u1, int v1, int w1)
{
    v[cnt] = v1, w[cnt] = w1;
    next[cnt] = first[u1], first[u1] = cnt++;
}

typedef pair<__int64,int> pii;
priority_queue<pii, vector<pii>, greater<pii> > q;

void Dijkstra(int src)
{
    bool done[MAXN] = {0};
    for(int i = 1; i <= n; i++) d[i] = (i == src)? 0:INF;
    q.push(make_pair(d[src], src));
    while(!q.empty())
    {
        pii u = q.top(); q.pop();
        int x = u.second;
        if(done[x]) continue;
        done[x] = 1;
        for(int e = first[x]; e != -1; e = next[e]) if(d[v[e]] > d[x]+w[e])
        {
            d[v[e]] = d[x] + w[e];
            q.push(make_pair(d[v[e]], v[e]));
        }
    }
}

int main()
{
    int T;
    scanf("%d", &T);
    while(T--)
    {
        init();
        __int64 tot = 0;
        scanf("%d%d", &n, &m);
        for(int i = 1; i <= m; i++)
        {
            int u1, v1;
            __int64 w1;
            scanf("%d%d%I64d", &u1, &v1, &w1);
            su[i] = u1, sv[i] = v1, sw[i] = w1;
            read_graph(u1, v1, w1);
        }
        Dijkstra(1);
        for(int i = 1; i <= n; i++) tot += d[i];
        init();
        for(int i = 1; i <= m; i++)
        {
            read_graph(sv[i], su[i], sw[i]);
        }
        Dijkstra(1);
        for(int i = 1; i <= n; i++) tot += d[i];
        printf("%I64d\n", tot);
    }
}