Submission #64567

#	Time	Username	Problem	Language	Result	Execution time	Memory
64567		qkxwsm	Beads and wires (APIO14_beads)	C++17	0 / 100	4 ms	2688 KiB

beads

/*
PROG: source
LANG: C++11
    _____
  .'     '.
 /  0   0  \
|     ^     |
|  \     /  |
 \  '---'  /
  '._____.'
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;

struct chash
{
        int operator()(int x) const
        {
                x ^= (x >> 20) ^ (x >> 12);
                return x ^ (x >> 7) ^ (x >> 4);
        }
        int operator()(long long x) const
        {
                return x ^ (x >> 32);
        }
};

template<typename T> using orderedset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename U> using hashtable = gp_hash_table<T, U, chash>;

template<class T>
void readi(T &x)
{
	T input = 0;
	bool negative = false;
	char c = ' ';
	while (c < '-')
        {
		c = getchar();
	}
	if (c == '-')
	{
		negative = true;
		c = getchar();
	}
	while (c >= '0')
	{
		input = input * 10 + (c - '0');
		c = getchar();
	}
	if (negative)
	{
		input = -input;
	}
	x = input;
}
template<class T>
void printi(T output)
{
	if (output == 0)
	{
		putchar('0');
		return;
	}
	if (output < 0)
	{
		putchar('-');
		output = -output;
	}
	int aout[20];
	int ilen = 0;
	while(output)
	{
		aout[ilen] = ((output % 10));
		output /= 10;
		ilen++;
	}
	for (int i = ilen - 1; i >= 0; i--)
	{
		putchar(aout[i] + '0');
	}
	return;
}
template<class T>
void ckmin(T &a, T b)
{
	a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
	a = max(a, b);
}
template<class T, class U>
T normalize(T x, U mod = 1000000007)
{
	return (((x % mod) + mod) % mod);
}
long long randomizell(long long mod)
{
	return ((1ll << 45) * rand() + (1ll << 30) * rand() + (1ll << 15) * rand() + rand()) % mod;
}
int randomize(int mod)
{
	return ((1ll << 15) * rand() + rand()) % mod;
}

#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << x << endl;

const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-10;

#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 100013

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;

int N;
vector<pii> edge[MAXN];
int parent[MAXN];
int dp[MAXN][2];

void dfs(int u)
{
        // cerr << "dfs " << u << endl;
        for (pii p : edge[u])
        {
                int d = p.fi, v = p.se;
                if (v == parent[u])
                {
                        continue;
                }
                parent[v] = u;
                dfs(v);
        }
        return;
}
void solve(int u)
{
        // cerr << "solve " << u << endl;
        int dup = -INF;
        for (pii p : edge[u])
        {
                int d = p.fi, v = p.se;
                if (v == parent[u])
                {
                        dup = d;
                        continue;
                }
                solve(v);
        }
        dp[u][1] = dup;
        int incr = -INF;
        for (pii p : edge[u])
        {
                int d = p.fi, v = p.se;
                if (v == parent[u]) continue;
                dp[u][1] += dp[v][1];
                ckmax(incr, dp[v][0] + d - dp[v][1]);
        }
        dp[u][1] += incr;
        int incr1 = -INF, incr2 = -INF;
        for (pii p : edge[u])
        {
                int d = p.fi, v = p.se;
                if (v == parent[u]) continue;
                dp[u][0] += dp[v][1];
                int gain = dp[v][0] + d - dp[v][1];
                if (gain > incr1)
                {
                        incr2 = incr1;
                        incr1 = gain;
                }
                else if (gain > incr2)
                {
                        incr2 = gain;
                }
        }
        dp[u][0] += max(0, incr2 + incr1);
        ckmax(dp[u][1], dp[u][0]);
        return;
}
int32_t main()
{
	ios_base::sync_with_stdio(0);
	srand(time(0));
	//	cout << fixed << setprecision(10);
	//	cerr << fixed << setprecision(10);
	if (fopen("input.in", "r"))
	{
		freopen ("input.in", "r", stdin);
		freopen ("output.out", "w", stdout);
	}
        cin >> N;
        if (N == 1)
        {
                cout << "0\n"; return 0;
        }
        for (int i = 1; i < N; i++)
        {
                int u, v, d;
                cin >> u >> v >> d;
                u--; v--;
                edge[u].PB({d, v});
                edge[v].PB({d, u});
        }
        dfs(0);
        solve(0);
        cout << dp[0][0] << '\n';
        //basically, choose edges so that no vertex has incidence more than 2
	//	cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
	return 0;
}

Compilation message (stderr)

beads.cpp: In function 'void dfs(int)':
beads.cpp:153:21: warning: unused variable 'd' [-Wunused-variable]
                 int d = p.fi, v = p.se;
                     ^
beads.cpp: In function 'int32_t main()':
beads.cpp:216:11: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen ("input.in", "r", stdin);
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
beads.cpp:217:11: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen ("output.out", "w", stdout);
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~

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