【Codeforces Alpha Round #20 C】Dijkstra?

题目链接

链接

翻译

让你求出 (1) 到 (n) 的最短路，打印路径。

题解

最短路堆优化。

记得 (dis) 数组开 (long long), 不然溢出会导致 (TLE) 问题 >_<

代码 (1) 是 (multiset) 写法。
代码 (2) 是 (priority queue) 写法。

代码1

#include <bits/stdc++.h>
#define LL long long
using namespace std;

struct abc{
    int id;
    LL dis;
    bool operator<(const abc &b)const{
        if (dis < b.dis){
            return true;
        }else if (dis == b.dis && id < b.id){
            return true;
        }
        return false;
    }
};

const int N = 1e5;
LL dis[N+10];
int n,m,pre[N + 10];
vector<pair<int,int> > g[N+10];
bool vis[N + 10];
multiset<abc> myset;

void dfs(int n){
    if (n == 0){
        return;
    }
    dfs(pre[n]);
    cout << n <<" ";
}

int main(){
    ios::sync_with_stdio(0),cin.tie(0);
    cin >> n >> m;
    for (int i = 1;i <= m; i++){
        int x,y,z;
        cin >> x >> y >> z;
        g[x].push_back(make_pair(y,z));
        g[y].push_back(make_pair(x,z));
    }
    memset(dis,255,sizeof dis);
    dis[1] = 0;
    abc temp;
    temp.dis = 0;temp.id = 1;
    myset.insert(temp);
    while (!myset.empty()){
        abc tmp = *(myset.begin());
        myset.erase(myset.begin());
        int x = tmp.id;
        for (pair<LL,int> temp:g[x]){
            int y = temp.first,w = temp.second;
            if (dis[y] == -1 || dis[y] > dis[x] + w){
                abc tmp;
                if (dis[y] != -1){
                    tmp.dis = dis[y];tmp.id = y;
                    myset.erase(myset.find(tmp));
                }
                dis[y] = dis[x] + w;
                pre[y] = x;
                tmp.id = y;tmp.dis = dis[y];
                myset.insert(tmp);
            }
        }
    }
    if (dis[n] == -1){
        cout << -1 << endl;
    }else{
        dfs(n);
    }
    return 0;
}

代码2

#include <bits/stdc++.h>
#define LL long long
using namespace std;

const int N = 1e5;
LL dis[N+10];
int n,m,pre[N + 10];
vector<pair<int,int> > g[N+10];
priority_queue<pair<LL,int>,vector<pair<LL,int> >,greater<pair<LL,int> > > pq;

void dfs(int n){
    if (n == 0){
        return;
    }
    dfs(pre[n]);
    cout << n <<" ";
}

int main(){
    ios::sync_with_stdio(0),cin.tie(0);
    cin >> n >> m;
    for (int i = 1;i <= m; i++){
        int x,y,z;
        cin >> x >> y >> z;
        g[x].push_back(make_pair(y,z));
        g[y].push_back(make_pair(x,z));
    }
    memset(dis,255,sizeof dis);
    dis[1] = 0;
    pq.push(make_pair(0,1));
    while (!pq.empty()){
        pair<LL,int> tmp = pq.top();
        pq.pop();
        int x = tmp.second;
        if (dis[x]!= -1 && dis[x] < tmp.first){
            continue;
        }
        for (pair<LL,int> temp:g[x]){
            int y = temp.first,w = temp.second;
            if (dis[y] == -1 || dis[y] > dis[x] + w){
                dis[y] = dis[x] + w;
                pre[y] = x;
                pq.push(make_pair(dis[y],y));
            }
        }
    }
    if (dis[n] == -1){
        cout << -1 << endl;
    }else{
        dfs(n);
    }
    return 0;
}