Submission #525667

#	Time	Username	Problem	Language	Result	Execution time	Memory
525667		qwerasdfzxcl	Mountains and Valleys (CCO20_day1problem3)	C++14	3 / 25	1689 ms	13120 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, cyc;
bool dfs0(int s, int e, int pa = -1){
    cyc.push_back(s);
    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();
        cyc.pop_back();
    }
    return 0;
}
 
int MX, IDX;
void dfs(int s, int pa = -1, int w = 0){
    if (pa==-1) dist[s] = 0;
    else dist[s] = dist[pa] + w;
 
    if (dist[s]>MX){
        MX = dist[s], IDX = s;
    }
    for (auto &v:adj[s]) if (v.v!=pa && on[v.i]) dfs(v.v, s, v.w);
}
 
int cur = 0, ans = 1e9;
int calc(int s, int n){
    MX = 0, IDX = s;
    dfs(s);
    if (MX==0) return 0;
 
    MX = 0;
    dfs(IDX);
 
    return MX;
}
 
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);
    }
 
    ans = min(ans, cur*2 - calc(0, n));
 
    //if (n>500) {printf("%d\n", ans); return 0;}
 
    for (auto &e:E){
        P.clear();
        cyc.clear();
        assert(dfs0(e.v, e.w));
 
        cur += W[e.i];
        int len = W[e.i] + P.size();
 
        for (auto &x:P) on[x] = 0;
 
        ///cycle
        //for (auto &x:cyc) ans = min(ans, cur*2 - len - calc(x, n));
 
        ///tree
        vector<int> deep, mx(cyc.size(), -1e9);
        for (auto &x:cyc){
            MX = 0, IDX = x;
            dfs(x);
            deep.push_back(MX);
        }
 
        for (int i=(int)cyc.size()-1;i>=0;i--){
            if (i+1<(int)cyc.size()) mx[i] = mx[i+1];
            mx[i] = max(mx[i], deep[i]-i);
        }
 
        for (int i=0;i<(int)cyc.size()-1;i++){
            ans = min(ans, (cur-1)*2 - (len + deep[i] + i + mx[i+1]));
        }
 
        ///
 
        for (auto &x:P) on[x] = 1;
 
        cur -= W[e.i];
    }
 
    printf("%d\n", ans);
    return 0;
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:52:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   52 |     scanf("%d %d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~~
Main.cpp:55:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   55 |         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