Submission #31617

#	Time	Username	Problem	Language	Result	Execution time	Memory
31617		ngkan146	Beads and wires (APIO14_beads)	C++98	0 / 100	6 ms	5120 KiB

beads

#include <bits/stdc++.h>
using namespace std;
struct edge{
    int v,w;
    edge(int v=0,int w=0): v(v), w(w) {}
};
int n;
vector <edge> G[200005];
int dp[200005][5];
inline int val1(int pos,int w){
    return dp[pos][0] + w;
}
inline int val02(int pos,int w){
    return max(dp[pos][0], dp[pos][2] + w);
}
void dfs(int u,int p){
    for(int i=0;i<G[u].size();i++){
        int v = G[u][i].v;
        if (v == p) continue;
        dfs(v,u);
    }
    // dp[i][0]
    dp[u][0] = 0;
    for(int i=0;i<G[u].size();i++){
        int v = G[u][i].v;
        if (v == p) continue;
        dp[u][0] += val02(v,G[u][i].w);
    }
    // dp[i][1]
    int fi02=0,se02=0,fiva02=-(int)1e9, seva02=-(int)1e9;
    for(int i=0;i<G[u].size();i++){
        int v = G[u][i].v;
        int w = G[u][i].w;
        if (v == p) continue;
        //cout << "UV" << u << ' ' << v << ' ' << val1(v,w) - val02(v,w) << endl;
        if (val1(v,w) - val02(v,w) >= val1(fi02,fiva02) - val02(fi02,fiva02))
            se02 = fi02,
            seva02 = fiva02,
            fi02 = v,
            fiva02 = w;
        else if (val1(v,w) - val02(v,w) >= val1(se02,seva02) - val02(se02,seva02))
            se02 = v,
            seva02 = w;
    }
    dp[u][1] = - (int) 1e9;
    if (se02){
        //cout << "u " << u << ' ' << fi02 << ' ' << se02 << endl;
        dp[u][1] = dp[u][0] - val02(fi02,fiva02) - val02(se02,seva02) + val1(fi02,fiva02) + val1(se02,seva02);
        for(int i=0;i<G[u].size();i++){
            int v = G[u][i].v;
            int w = G[u][i].w;
            if (v == p) continue;
            if (v != fi02)
                dp[u][1] = max(dp[u][1], dp[u][0] - val02(fi02,fiva02) + val1(fi02,fiva02) - val02(v,w) + w + dp[v][1]);
            else
                dp[u][1] = max(dp[u][1], dp[u][0] - val02(se02,seva02) + val1(se02,seva02) - val02(v,w) + w + dp[v][1]);
        }
    }
    // dp[i][2]
    dp[u][2] = -(int)1e9;
    for(int i=0;i<G[u].size();i++){
        int v = G[u][i].v;
        int w = G[u][i].w;
        if (v == p) continue;
        dp[u][2] = max(dp[u][2], dp[u][0] - val02(v,w) + max(dp[v][0],dp[v][1]) + G[u][i].w);
    }
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<n;i++){
        int x,y,w;
        scanf("%d %d %d",&x,&y,&w);
        G[x].push_back(edge(y,w));
        G[y].push_back(edge(x,w));
    }
    dfs(1,1);
    cout << max(dp[1][0], dp[1][1]) << endl;
    //for(int i=1;i<=n;i++)
    //    cout << "I " << i << ' ' << dp[i][0] <<' ' << dp[i][1] << ' ' << dp[i][2] << endl;
}
/*
10
4 10 2
1 2 21
1 3 13
6 7 1
7 9 5
2 4 3
2 5 8
1 6 55
6 8 34
10
4 10 5
1 10 7
3 10 10
3 9 10
2 3 5
3 8 9
7 10 3
5 8 9
4 6 6
*/

Compilation message (stderr)

beads.cpp: In function 'void dfs(int, int)':
beads.cpp:17:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<G[u].size();i++){
                 ~^~~~~~~~~~~~
beads.cpp:24:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<G[u].size();i++){
                 ~^~~~~~~~~~~~
beads.cpp:31:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<G[u].size();i++){
                 ~^~~~~~~~~~~~
beads.cpp:49:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<G[u].size();i++){
                     ~^~~~~~~~~~~~
beads.cpp:61:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<G[u].size();i++){
                 ~^~~~~~~~~~~~
beads.cpp: In function 'int main()':
beads.cpp:69:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~
beads.cpp:72:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d %d %d",&x,&y,&w);
         ~~~~~^~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 13
• Subtask 2: 0 / 15
• Subtask 3: 0 / 29
• Subtask 4: 0 / 43