洛谷p4479：單源最短路模板（使用鄰接表+堆優化的dijkstra算法）

題目傳送門

洛谷p4479

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解題思路

因爲數據量過大，無法使用普通的dijkstra算法以及鄰接矩陣來存圖，這裏我們可以使用鄰接表+堆優化的dijkstra算法，或者採用鏈式前向星+堆優化的dijkstra算法，這裏給出後者的代碼。

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Code

#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int N = 1e5 + 5;
const int M = 2e5 + 5;
typedef pair<int, int> P;
struct Edge {
    int next, to, w;
}edge[M];  
int n, m, st, ed, cnt;
int head[N], dis[N];
bool vis[N];

inline void init()
{
    cnt = 0;
    memset(head, -1, sizeof head);
    memset(dis, INF, sizeof dis);
    memset(vis, false, sizeof vis);
}

inline void add(int u, int v, int w)
{
    edge[cnt].w = w;
    edge[cnt].to = v;
    edge[cnt].next = head[u];
    head[u] = cnt++;
}

void Dijkstra()
{
    priority_queue<P, vector<P>, greater<P> > q;
    dis[st] = 0;
    q.push({0, st});
    while(q.size()) {
        P now = q.top(); q.pop();
        int u = now.second;
        if(vis[u]) continue;
        vis[u] = true;
        for(int i = head[u]; ~i; i = edge[i].next) {
            int v = edge[i].to;
            if(!vis[v] && dis[v] > dis[u] + edge[i].w) {
                dis[v] = dis[u] + edge[i].w;
                q.push({dis[v], v});
            }
        }
    }
}

int main()
{
    int a, b, c;
    init();
    cin >> n >> m >> st;
    for(int i = 1; i <= m; ++i) {
        cin >> a >> b >> c;
        add(a, b, c);
    }
    Dijkstra();
    for(int i = 1; i <= n; ++i) {
        cout << dis[i] << " ";
    }
    cout << endl;
    return 0;
}