Submission #524852

#	Time	Username	Problem	Language	Result	Execution time	Memory
524852		qwerasdfzxcl	Mountains and Valleys (CCO20_day1problem3)	C++14	3 / 25	14 ms	12768 KiB

Main

#include <bits/stdc++.h>

typedef long long ll;
using namespace std;
struct Edge{
    int v, w, i;
    Edge(){}
    Edge(int _v, int _w, int _i): v(_v), w(_w), i(_i) {}
};
vector<Edge> adj[500500];
int on[2002000], W[2002000], dist[500500];
vector<Edge> E;

vector<int> P;
bool dfs0(int s, int e, int pa = -1){
    if (s==e) return 1;
    for (auto &v:adj[s]) if (v.v!=pa && on[v.i]){
        P.push_back(v.i);
        if (dfs0(v.v, e, s)) return 1;
        P.pop_back();
    }
    return 0;
}

int cnt;
void dfs(int s, int pa = -1, int w = 0){
    cnt++;
    if (pa==-1) dist[s] = 0;
    else dist[s] = dist[pa] + w;
    for (auto &v:adj[s]) if (v.v!=pa && on[v.i]) dfs(v.v, s, v.w);
}

int cur = 0, ans = 1e9;
void calc(int n){
    cnt = 0;
    dfs(0);
    assert(cnt==n);

    cnt = 0;
    dfs(max_element(dist, dist+n)-dist);
    assert(cnt==n);

    ans = min(ans, cur*2 - *max_element(dist, dist+n));
}

int main(){
    int n, m;
    scanf("%d %d", &n, &m);
    for (int i=1;i<=m;i++){
        int x, y, z;
        scanf("%d %d %d", &x, &y, &z);
        adj[x].emplace_back(y, z, i);
        adj[y].emplace_back(x, z, i);
        W[i] = z;

        if (z==1) on[i] = 1, cur++;
        else E.emplace_back(x, y, i);
    }

    calc(n);
    if (n>500) {printf("%d\n", ans); return 0;}

    for (auto &e:E){
        P.clear();
        dfs0(e.v, e.w);
        //printf("%d %d: ", e.v, e.w);
        //for (auto &x:P) printf("%d ", x);
        //printf("\n");
        if ((int)P.size()<=W[e.i]) continue;

        on[e.i] = 1, cur += W[e.i];

        for (auto &x:P){
            on[x] = 0, cur -= W[x];
            calc(n);
            on[x] = 1, cur += W[x];
        }
        on[e.i] = 0, cur -= W[e.i];
    }

    printf("%d\n", ans);
    return 0;
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:48:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   48 |     scanf("%d %d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~~
Main.cpp:51:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   51 |         scanf("%d %d %d", &x, &y, &z);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 1 / 1
• Subtask 2: 0 / 2
• Subtask 3: 2 / 2
• Subtask 4: 0 / 6
• Subtask 5: 0 / 2
• Subtask 6: 0 / 3
• Subtask 7: 0 / 5
• Subtask 8: 0 / 4