PAT--1003. Emergency (最短路)

题解

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
using namespace std;

const int maxn = 500 + 3;
const int inf  = 0x3f3f3f3f;
struct Edge{
int to, w;
};

struct Node{
int u, d;
bool operator < (const Node& rhs) const{
return d > rhs.d;
}
};
vector<Edge> G[maxn];
int n, m, s, t;
int a[maxn];
int pathNum[maxn];
int dist[maxn];
bool vis[maxn];
int teams[maxn];

void Dijkstra(int s){
for(int i = 0; i < n; ++i) dist[i] = inf;
priority_queue<Node> Q;
Q.push(Node{s, 0});
dist[s] = 0;
pathNum[s] = 1;
teams[s] = a[s];

while(!Q.empty()){
Node p = Q.top();
Q.pop();
int u = p.u;

if(vis[u]) continue;
vis[u] = true;
for(int i = 0; i < G[u].size(); ++i){
int v = G[u][i].to, d = G[u][i].w;
if(!vis[v]){
if(dist[v] > dist[u] + d){
pathNum[v] = pathNum[u];
dist[v] = dist[u] + d;
teams[v] = teams[u] + a[v];
Q.push(Node{v, dist[v]});
}
else if(dist[v] == dist[u] + d){
teams[v] = max(teams[v], teams[u] + a[v]);
pathNum[v] += pathNum[u];
}
}
}
}
cout << pathNum[t] << " " << teams[t] << endl;
}

// brute force searching every path !!!
int cnt, maxteams, mindist = inf;
void dfs(int u, int d, int teams){
if(u == t){
if(d < mindist) mindist = d, cnt = 1, maxteams = teams;
else if(d == mindist) cnt++, maxteams = max(maxteams, teams);
return;
}
vis[u] = true;
for(int i = 0; i < G[u].size(); ++i){
int v = G[u][i].to, w = G[u][i].w;
if(!vis[v]) dfs(v, d + w, teams + a[v]);
}
vis[u] = false;
}

int main(){
#ifdef EXMY
freopen("data.in", "r", stdin);
#endif

cin >> n >> m >> s >> t;
for(int i = 0; i < n; ++i) cin >> a[i];
while(m--){
int u, v, w;
cin >> u >> v >> w;
G[u].push_back(Edge{v, w});
G[v].push_back(Edge{u, w});
}
Dijkstra(s);
//    dfs(s, 0, a[s]);
//    cout << cnt << " " << maxteams << endl;
return 0;
}