Submission #992399

#	Time	Username	Problem	Language	Result	Execution time	Memory
992399		yeediot	Beads and wires (APIO14_beads)	C++17	100 / 100	84 ms	27012 KiB

beads

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define pb push_back
#define sz(x) (int)(x.size())
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
#define vi vector<int>
#define vp vector<pii>
#define vvi vector<vi>
#define ykh mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count())
#define __lg(x) 63-__builtin_clzll(x)
#define pow2(x) (1LL<<x)
void __print(int x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
void setIO(string s) {
    freopen((s + ".in").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
}
#ifdef local
void CHECK();
void setio(){
    freopen("/Users/iantsai/cpp/input.txt","r",stdin);
    freopen("/Users/iantsai/cpp/output.txt","w",stdout);
}
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
void setio(){}
#define debug(x...)
#endif
#define TOI_is_so_de ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);setio();
int n;
const int mxn = 2e5+5;
const int inf = -1e18;
vector<pii>adj[mxn];
int dp[mxn], ans = 0;
pii dp2[mxn][2];
void dfs(int v,int pa){
    int sum = 0;
    for(auto [u, d] : adj[v]){
        if(u == pa) continue;
        dfs(u, v);
        dp[v] += max(dp[u], dp2[u][0].F+d);
    }
    for(auto [u, d] : adj[v]){
        if(u == pa) continue;
        pii p = {dp[v]-max(dp[u], dp2[u][0].F+d)+d+dp[u], u};
        auto &x=dp2[v];
        if(p.F >= x[0].F){
            x[1] = x[0];
            x[0] = p;
        }
        else if(p.F > x[1].F){
            x[1] = p;
        }
    }
    if(sz(adj[v])==1 and pa!=v){
        dp2[v][0]={inf,inf};
        dp2[v][1]={inf,inf};
    }
}
void cal(int v,int pa){
    chmax(ans, dp[v]);
    for(auto [u, d] : adj[v]){
        if(u == pa) continue;
        auto p = dp2[v];
        auto x = dp[v];
        dp[v] -= max(dp[u], dp2[u][0].F+d);
        auto p1 = dp2[v][0];
        if(p1.S == u) p1 = dp2[v][1];
        p1.F -= max(dp[u], dp2[u][0].F+d);
        dp[u] += max(dp[v], p1.F+d);
        dp2[u][0].F += max(dp[v], p1.F+d);
        dp2[u][1].F += max(dp[v], p1.F+d);
        pii p2 = {dp[u]-max(dp[v], p1.F+d)+d+dp[v], v};
        if(p2.F >= dp2[u][0].F){
            dp2[u][1] = dp2[u][0];
            dp2[u][0] = p2;
        }
        else if(p2.F >= dp2[u][1].F){
            dp2[u][1] = p2;
        }
        cal(u,v);
        dp[v] = x;
        dp2[v][0]=p[0];
        dp2[v][1]=p[1];
    }
}
signed main(){
    TOI_is_so_de;
    cin >> n;
    for(int i=1;i<n;i++){
        int a, b, c;
        cin >> a >> b >> c;
        adj[a].pb({b,c});
        adj[b].pb({a,c});
    }
    for(int i=1;i<=n;i++){
        for(int j=0;j<2;j++){
            dp2[i][j]={inf,inf};
        }
    }
    dfs(1,1);
    cal(1,1);
    cout << ans << '\n';
    #ifdef local
    CHECK();
    #endif
}
/*
*/
#ifdef local
void CHECK(){
    cerr << "\n[Time]: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms.\n";
     function<bool(string,string)> compareFiles = [](string p1, string p2)->bool {
         std::ifstream file1(p1);
         std::ifstream file2(p2);
         if (!file1.is_open() || !file2.is_open())return false;
         std::string line1, line2;
         while (getline(file1, line1) && getline(file2, line2)) {
             if (line1 != line2)return false;
         }
         int cnta=0,cntb=0;
         while(getline(file1,line1))cnta++;
         while(getline(file2,line2))cntb++;
         return cntb-cnta<=1;
     };
     bool check = compareFiles("output.txt","expected.txt");
     if (check) cerr<<"ACCEPTED\n";
     else cerr<<"WRONG ANSWER!\n";
}
#else
#endif



 

Compilation message (stderr)

beads.cpp: In function 'void dfs(long long int, long long int)':
beads.cpp:57:9: warning: unused variable 'sum' [-Wunused-variable]
   57 |     int sum = 0;
      |         ^~~
beads.cpp: In function 'void setIO(std::string)':
beads.cpp:35:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   35 |     freopen((s + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
beads.cpp:36:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |     freopen((s + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 29 / 29
• Subtask 4: 43 / 43