2018南京网络赛L题：Magical Girl Haze（最短路分层图）

题目链接：https://nanti.jisuanke.com/t/31001

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解题心得：

• 一个BZOJ的原题，之前就写过博客了。
  
  • 原题地址：https://www.lydsy.com/JudgeOnline/problem.php?id=2763
  • 原题博客：https://www.cnblogs.com/GoldenFingers/p/9574230.html
• 比赛的时候遇到这个题第一个反应就是原题，然后用了以前的代码，WA：单向边，以前代码上是双向边。TLE：这个题出题人还卡了一下网格图。

#include <stdio.h>
#include <cstring>
#include <algorithm>
#include <queue>
#include <vector>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
const int maxn = 1e6+100;
const ll INF = 1e12;

ll n, m, k, S, T;

struct edge {
    ll to, len;

    edge(ll to1, ll len1):
            to(to1), len(len1){};
};

struct NODE {
    ll len, pos, c;

    bool friend operator < (NODE a, NODE b) {
        return a.len > b.len;
    }

    NODE (ll len1, ll pos1, ll c1):
            len(len1), pos(pos1), c(c1){};
};

vector <edge> ve[maxn];

ll dis[11][maxn];

void add_edge(ll u, ll v, ll len) {
    ve[u].push_back(edge(v, len));
}

void init() {
    for(int i=0;i<11;i++)
        for(int j=0;j<maxn;j++)
            dis[i][j] = INF;

    scanf("%lld%lld%lld",&n,&m,&k);
    for(int i=0;i<=n;i++)
        ve[i].clear();
    S = 1, T = n;
    for(int i=0;i<m;i++) {
        ll u, v, len;
        scanf("%lld%lld%lld",&u, &v, &len);
        add_edge(u, v, len);
    }
}

void dij() {
    priority_queue <NODE> qu;
    qu.push(NODE(0, S, 0));
    dis[0][S] = 0;
    while(!qu.empty()) {
        NODE now = qu.top(); qu.pop();
        ll u = now.pos;
        for(int i=0;i<ve[u].size();i++) {
            ll v = ve[u][i].to;
            ll len = ve[u][i].len;
            ll c = now.c;
            if(dis[c][v] > dis[c][u]+len) {
                dis[c][v] = dis[c][u] + len;
                qu.push(NODE(dis[c][v], v, c));
            }
        }

        ll c = now.c;
        if(c < k) {
            for (int i = 0; i < ve[u].size(); i++) {
                ll v = ve[u][i].to;
                if(dis[c+1][v] > dis[c][u]) {
                    dis[c+1][v] = dis[c][u];
                    qu.push(NODE(dis[c][u], v, c+1));
                }
            }
        }
    }
}

void min_path() {
    dij();
    ll Min = INF;
    for(int i=0;i<=k;i++) {
        Min = min(Min, dis[i][T]);
    }
    printf("%lld
", Min);
}

int main() {
    int t;
    scanf("%d",&t);
    while(t--) {
        init();
        min_path();
    }
}

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