Submission #1255596

#	Time	Username	Problem	Language	Result	Execution time	Memory
1255596		thdh__	Cat Exercise (JOI23_ho_t4)	C++20	100 / 100	242 ms	61600 KiB

Main

#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define eb emplace_back
#define pu push
#define ins insert
#define fi first
#define se second
#define all(a) a.begin(),a.end()
#define bruh ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fu(x,a,b) for (auto x=a;x<=b;x++)
#define fd(x,a,b) for (auto x=a;x>=b;x--)
#define int ll

using namespace std;
//mt19937 mt(chrono::steady_clock::now().time_since_epoch().count());

/*
Competitive Programming notes that I need to study & fix my dumbass self:

1. Coding:
- Always be sure to check the memory of arrays (maybe use vectors), for loops
- Always try to maximize the memory if possible, even if you are going for subtasks
- Do not exploit #define int long long, it will kill you

2. Stress: 
- Always try generating big testcases and try if they run

3. Time management:
- Don't overcommit or undercommit, always spend a certain amount of time to think a problem, don't just look at it and say I'm fucked
- Do not spend too much time coding brute-force solutions, they should be easily-codable solutions that don't take up too much time

Time management schedule:
Offline / LAH days (4 problems - 3h):
15' thinking of solution / idea
1. no idea: skip
2. yes idea: continue thinking for <= 15'

+ implementing: <= 20'
+ brute-force: <= 5'
+ test generator: <= 5'

I hate offline because I am dumb
*/

typedef pair<int, int> ii;
const int N = 2e5+5;
const int M = 20;
const int B = 750;
const int mod = 1e9+7;
const int inf = 1e18;
using cd = complex<double>;
const long double PI = acos(-1);
int power(int a,int b) {ll x = 1;if (a >= mod) a%=mod; while (b) {if (b & 1) x = x*a % mod;a = a*a % mod;b>>=1;}return x;} 

int n;
int a[N], h[N];
vector<int> adj[N];
int up[N][M];
int dp[N];

void dfs(int u, int p) 
{
	up[u][0] = p;
	for (int i = 1; i < M; i++) up[u][i] = up[up[u][i-1]][i-1];
	for (auto v : adj[u]) 
	{
		if (v == p) continue;
		h[v] = h[u] + 1;
		dfs(v, u);
	}
}

int lca(int u, int v) 
{
	if (h[u] < h[v]) swap(u,v);
	int diff = h[u] - h[v];
	for (int i = 0; i < M; i++) if (diff>>i & 1) u = up[u][i];
	if (u == v) return u;
	for (int i = M-1; i >= 0; i--) if (up[u][i] != up[v][i]) u = up[u][i], v = up[v][i];;
	return up[u][0];
}

int dist(int u, int v) 
{
	return h[u] + h[v] - 2 * h[lca(u,v)];
}

int par[N], sz[N];

int find(int u) 
{
	if (u == par[u]) return u;
	return par[u] = find(par[u]);
}

void merge(int u, int v) 
{
	u = find(u), v = find(v);
	if (u == v) return;
	if (a[u] < a[v]) swap(u,v);
	par[v] = u;
	sz[u] += sz[v];
}

bool cmp(int i, int j) 
{
	return a[i] < a[j];
}

void solve()
{
	cin>>n;
	int root = 0;
	for (int i = 1; i <= n; i++) 
	{
		cin>>a[i];
		if (a[i] == n) root = i;
	}
	for (int i = 1; i < n; i++) 
	{
		int u,v; cin>>u>>v;
		adj[u].pb(v); adj[v].pb(u);
	}
	dfs(1, 0);
	vector<int> id;
	for (int i = 1; i <= n; i++) 
	{
		id.pb(i);
		par[i] = i; sz[i] = 1;
	}
	sort(all(id), cmp);
	for (int i = 0; i < n; i++) 
	{
		int u = id[i];
		for (auto v : adj[u]) 
		{
			if (a[v] > a[u]) continue;
			v = find(v);
			dp[u] = max(dp[u], dp[v] + dist(u, v));
			merge(u, v);
		}
	}
	cout<<dp[root];
}

/*
Go through the mistakes you usually make and revise your code, for god's sake...
*/

signed main()
{
	bruh
	//freopen("input.inp","r",stdin);
	//freopen("output.inp","w",stdout);
	int t = 1;
	// cin>>t;
	while (t--)
	{
		solve();
		cout<<"\n";
	}
}

• Subtask 1: 7 / 7
• Subtask 2: 7 / 7
• Subtask 3: 7 / 7
• Subtask 4: 10 / 10
• Subtask 5: 20 / 20
• Subtask 6: 23 / 23
• Subtask 7: 26 / 26