Roadblocks POJ - 3255 (次短路）

https://vjudge.net/problem/POJ-3255

 

#include <iostream>
#include <cstring>
#include <queue>
#include <vector>
using namespace std;
typedef pair<int, int> P;
const int N = 2e5 + 10;
struct Edge {
    int to, next, w;
}edge[N];

int head[N], dis1[N], dis2[N];
int cnt, n, r;

priority_queue<P, vector<P>, greater<P> > q;

//链式前向星
void addEdge(int u, int v, int cost) {
    edge[++cnt].to = v;
    edge[cnt].w = cost;
    edge[cnt].next = head[u];
    head[u] = cnt;
}

void dijkstra(int s) {
    dis1[s] = 0;
    q.push(P(0, s));
    while(!q.empty()) {
        P t = q.top();
        q.pop();
        int d = t.first, cur = t.second;
        if(dis2[cur] < d) continue;
        for(int i = head[cur]; i != - 1; i = edge[i].next) { //搜边
            int d2 = d + edge[i].w, u = edge[i].to;
            if(d2 < dis1[u]) {  //更新最短路径前更新次短路径
                dis2[u] = dis1[u];
                dis1[u] = d2;
                q.push(P(dis1[u], u));
            }
            if(d2 > dis1[u] && d2 < dis2[u]) { //再次判断次短路出现的情况
                dis2[u] = d2;
                q.push(P(dis2[u], u));
            }
        }
    }
}

int main() {
    ios::sync_with_stdio(0);
    memset(head, -1, sizeof(head));
    memset(dis1, 0x3f, sizeof(dis1));
    memset(dis2, 0x3f, sizeof(dis2));
    int u, v, c;
    cin >> n >> r;
    for(int i = 1; i <= r; i++) {
        cin >> u >> v >> c;
        addEdge(u, v, c);
        addEdge(v, u, c);
    }
    dijkstra(1);
    cout << dis2[n];
    return 0;
}