AcWing850.Dijkstra求最短路 II

題解

#include <iostream>
#include <cstring>
#include <queue>
#include <vector>
using namespace std;

const int N = 1e6 + 10;

typedef pair<int,int> PII;
bool flag[N];
int d[N];
int h[N], e[N], ne[N], v[N], idx;

void add(int x, int y, int z)
{
    ne[idx] = h[x], h[x] = idx, e[idx] = y, v[idx++] = z; 
}

void Dijkstra()
{
    memset(d, 0x3f, sizeof d);
    d[1] = 0;
    priority_queue<PII, vector<PII>, greater<PII>> q;
    q.push({d[1], 1});
    while(q.size())
    {
        int head = q.top().second, distance = q.top().first;
        q.pop();
        if(flag[head]) continue;
        flag[head] = true;
        for(int i = h[head]; ~i; i = ne[i])
            if(!flag[e[i]] && distance + v[i] < d[e[i]])
                d[e[i]] = v[i] + distance, q.push({d[e[i]], e[i]});
    }
}

int main()
{
    memset(h, -1, sizeof h);
    int n, m, x, y, z;
    scanf("%d%d",&n,&m);
    for(int i = 1; i <= m; ++i)
        scanf("%d%d%d",&x,&y,&z), add(x, y, z);
    Dijkstra();
    if(flag[n])
        cout << d[n] << endl;
    else
        cout << -1 << endl;
    return 0;
}