【模板】单源最短路径 堆优化的dijkstra

 

堆优化的dij 

先放代码去瞅一眼牛客网比赛qwq

#include<queue> 
#include<cstdio>
#include<iostream>
using namespace std;
const int maxn = 100010, maxm = 500020, inf = 1<<30;
int num = 0, n, m, s;
int head[maxm], dis[maxn];
bool vis[maxn];
priority_queue< pair<int, int> >q;
struct edge {
    int nxt, to, dis;
}e[maxm<<1];
int read() {
    char ch = getchar(); int x = 0, f = 1;
    while(ch<'0'||ch>'9') {if(ch == '-') f = -1;ch = getchar();}
    while(ch>='0'&&ch<='9') {x = x*10+ch-'0'; ch = getchar();}
    return x*f;
}
void add(int from, int to, int dis) {
    e[++num].nxt = head[from];
    e[num].to = to;
    e[num].dis = dis;
    head[from] = num;
}
void dijkstra() {
    for(int i = 1; i <= n; i++) {
        dis[i] = inf;
        vis[i] = 0;
    }
//    vis[s] = 1;
    dis[s] = 0;
    q.push(make_pair(0, s));
    while(q.size()) {
        int u = q.top().second;
        q.pop();
        if(vis[u]) continue;
        vis[u] = 1;
        for(int i = head[u]; i; i = e[i].nxt) {
            int v = e[i].to;
            if(dis[v] > dis[u]+e[i].dis) {
                dis[v] = dis[u]+e[i].dis;
                q.push(make_pair(-dis[v], v));
            }
        }
    }
}

int main() {
    scanf("%d%d%d", &n, &m, &s);
    for(int i = 1; i <= m; i++) {
        int f, g, k;
        f = read(), g = read(), k = read();
        add(f, g, k);
    }
    dijkstra();
    for(int i = 1; i <= n; i++) 
        printf("%d ", dis[i]);
    return 0;
}

 如果把起点初始为1，已经访问过就直接结束了QAQ 和spfa不一样！！

第42行， 放进堆里的是dis[v] 的相反数， 因为priority_queue初始大根堆， 这样就不用重定义小根堆了qwq