【luogu P1608 路径统计】 题解

题目链接：https://www.luogu.org/problemnew/show/P1608

补上一发最短路计数！

感谢王强qwqqqq @Lance1ot

#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 200010;
int dis[maxn], ans[maxn], n, m, k, used[2010][2010];
bool vis[maxn];
struct edge{
    int next, to, len;
}e[maxn<<2];
int head[maxn], cnt;
queue<int> q;
void add(int u, int v, int w)
{
    e[++cnt].len = w;
    e[cnt].next = head[u];
    e[cnt].to = v;
    head[u] = cnt;
}
void SPFA()
{
    while(!q.empty())
    {
        int now = q.front(); q.pop();
        vis[now] = 0;
        if(now == n) continue;
        for(int i = head[now]; i != -1; i = e[i].next)
        {
            if(dis[e[i].to] == dis[now] + e[i].len)
            {
                ans[e[i].to] = (ans[e[i].to] + ans[now]);
                if(!vis[e[i].to])
                {
                    q.push(e[i].to);
                    vis[e[i].to] = 1;
                }
            }
            if(dis[e[i].to] > dis[now] + e[i].len)
            {
                dis[e[i].to] = dis[now] + e[i].len;
                ans[e[i].to] = ans[now];
                if(!vis[e[i].to])
                {
                    q.push(e[i].to);
                    vis[e[i].to] = 1;
                }
            }
        }
        ans[now]=0;
    }
}
int main()
{
        memset(head, -1, sizeof(head));
        memset(dis, 127, sizeof(dis));
        memset(used, 127, sizeof(used));
        while(!q.empty()) q.pop();
        scanf("%d%d",&n,&m);
        for(int i = 1; i <= m; i++)
        {
            int u, v, w;
            scanf("%d%d%d",&u,&v,&w);
            if(used[u][v] > w)
            {
                add(u, v, w);
                used[u][v] = w;
            }
        }
        dis[1] = 0;
        vis[1] = 1;
        ans[1] = 1;
        q.push(1);
        SPFA();
        if(dis[n] >= 2139062143) {printf("No answer\n"); return 0;}
        printf("%d %d\n",dis[n], ans[n]);
}