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ICPC 2018 南京网络赛 J Magical Girl Haze(多层图最短路)

时间:2019-03-28 13:53:25      阅读:194      评论:0      收藏:0      [点我收藏+]

标签:spl   ref   its   push   ||   sync   style   bug   getc   

传送门:https://nanti.jisuanke.com/t/A1958

题意:n个点m条边的路,你有k次机会将某条路上的边权变为0,问你最短路径长度

题解:最短路变形,我们需要在常规的最短路上多开 一维,记录,我消耗j次机会时的最短路径长度为多少

代码:

技术图片
/**
 *        ┏┓    ┏┓
 *        ┏┛┗━━━━━━━┛┗━━━┓
 *        ┃       ┃  
 *        ┃   ━    ┃
 *        ┃ >   < ┃
 *        ┃       ┃
 *        ┃... ⌒ ...  ┃
 *        ┃       ┃
 *        ┗━┓   ┏━┛
 *          ┃   ┃ Code is far away from bug with the animal protecting          
 *          ┃   ┃   神兽保佑,代码无bug
 *          ┃   ┃           
 *          ┃   ┃        
 *          ┃   ┃
 *          ┃   ┃           
 *          ┃   ┗━━━┓
 *          ┃       ┣┓
 *          ┃       ┏┛
 *          ┗┓┓┏━┳┓┏┛
 *           ┃┫┫ ┃┫┫
 *           ┗┻┛ ┗┻┛
 */
#include <set>
#include <map>
#include <deque>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <bitset>
#include <cstdio>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

typedef long long LL;
typedef pair<LL, LL> pLL;
typedef pair<LL, int> pLi;
typedef pair<int, LL> pil;;
typedef pair<int, int> pii;
typedef unsigned long long uLL;
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define bug printf("*********\n")
#define FIN freopen("input.txt","r",stdin);
#define FON freopen("output.txt","w+",stdout);
#define IO ios::sync_with_stdio(false),cin.tie(0)
#define debug1(x) cout<<"["<<#x<<" "<<(x)<<"]\n"
#define debug2(x,y) cout<<"["<<#x<<" "<<(x)<<" "<<#y<<" "<<(y)<<"]\n"
#define debug3(x,y,z) cout<<"["<<#x<<" "<<(x)<<" "<<#y<<" "<<(y)<<" "<<#z<<" "<<z<<"]\n"
LL read() {
    int x = 0, f = 1; char ch = getchar();
    while(ch < 0 || ch > 9) {
        if(ch == -)f = -1;
        ch = getchar();
    }
    while(ch >= 0 && ch <= 9) {
        x = x * 10 + ch - 0;
        ch = getchar();
    }
    return x * f;
}
const double eps = 1e-8;
const int mod = 1e9 + 7;
const int maxn = 3e5 + 5;
const int INF = 0x3f3f3f3f;
const LL INFLL = 0x3f3f3f3f3f3f3f3f;
struct EDGE {
    int v, nxt, w;
} edge[maxn];
int head[maxn];
int tot;
void add_edge(int u, int v, int w) {
    edge[tot].v = v;
    edge[tot].w = w;
    edge[tot].nxt = head[u];
    head[u] = tot++;
}
struct node {
    int u;
    LL dis;
    int cnt;
    node() {}
    node(int u1, int dis1, int cnt1) {
        u = u1, dis = dis1, cnt = cnt1;
    }
    bool operator < (const node &a) const {
        return a.dis < dis;
    }
};
LL dis[maxn][15];
LL vis[maxn][15];
LL dij(int st, int ed, int k) {
    memset(dis, INF, sizeof(dis));
    memset(vis, 0, sizeof(vis));
    priority_queue<node> q;
    dis[st][0] = 0;
    q.push(node(st, 0, 0));
    while(!q.empty()) {
        node tmp = q.top();
        q.pop();
        int u = tmp.u;
        int cnt = tmp.cnt;
        if(u == ed) {
            return tmp.dis;
        }
        if(vis[u][cnt]) continue;
        vis[u][cnt] = 1;
        for(int i = head[u]; i != -1; i = edge[i].nxt) {
            int v = edge[i].v;
            if(dis[v][cnt] > dis[u][cnt] + edge[i].w) {
                dis[v][cnt] = dis[u][cnt] + edge[i].w;
                q.push(node(v, dis[v][cnt], cnt));
            }
            if (cnt + 1 <= k && !vis[v][cnt + 1] && dis[u][cnt] < dis[v][cnt + 1]) { // 当前边权为0,状态更新
                dis[v][cnt + 1] = dis[u][cnt];
                q.push(node(v, dis[v][cnt + 1], cnt + 1));
            }
        }

    }
    return -1;
}

int main() {
#ifndef ONLINE_JUDGE
    FIN
#endif
    int T;
    scanf("%d", &T);
    while(T--) {
        int n, m, k;
        memset(head, -1, sizeof(head));
        tot = 0;
        scanf("%d%d%d", &n, &m, &k);
        for(int i = 1, u, v, w; i <= m; i++) {
            scanf("%d%d%d", &u, &v, &w);
            add_edge(u, v, w);
        }
        LL ans = INF;
        for (int i = 0; i <= k; ++i) // 0 到 k
            ans = min(ans, dij(1, n, i));
        printf("%lld\n", ans);
    }
    return 0;
}
View Code

 

ICPC 2018 南京网络赛 J Magical Girl Haze(多层图最短路)

标签:spl   ref   its   push   ||   sync   style   bug   getc   

原文地址:https://www.cnblogs.com/buerdepepeqi/p/10614199.html

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