Submission #72335

#	Time	Username	Problem	Language	Result	Execution time	Memory
72335		nvmdava	Dreaming (IOI13_dreaming)	C++17	100 / 100	280 ms	34152 KiB

dreaming

#include "dreaming.h"
#include <bits/stdc++.h>
using namespace std;

struct Path{
	int to, cost;
	Path(int _to, int _cost){
		to = _to;
		cost = _cost;
	}
};

struct Node{
	int p[20], d;
};
map<int, int> c[100001];
vector<Path> path[100001];
bool in[100001];
Node a[100001];
int mxdist, mxid;
int solo = 0;
void build(int v, int p){
	in[v] = 1;
	for(auto x : path[v]){
		if(x.to == p) continue;
		a[x.to].d = a[v].d + 1;
		memset(a[x.to].p, -1, sizeof(a[x.to].p));
		a[x.to].p[0] = v;
		for(int i = 1; i < 20; i++){
			int t = a[x.to].p[i - 1];
			if(t == -1) break;
			a[x.to].p[i] = a[t].p[i - 1];
		}
		build(x.to, v);
	}
}

int goUp(int v, int u){
	for(int i = 0; i < 20; i++){
		if(u & (1 << i)) v = a[v].p[i];
	}
	return v;
}

int lca(int v, int u){
	int l = 0;
	int r = min(a[v].d, a[u].d) + 1;
	int m;
	while(l + 1 != r){
		m = (l + r) >> 1;
		if(goUp(v, a[v].d - m) == goUp(u, a[u].d - m)) l = m;
		else r = m;
	}
	return goUp(v, a[v].d - l);
}

void dfs(int v, int p, int d){
	if(path[v].size() == 1 && p != -1){
		if(d > mxdist){
			mxdist = d;
			mxid = v;
		}
	}
	for(auto x : path[v]){
		if(x.to == p) continue;
		dfs(x.to, v, d + x.cost);
	}
}

int comp = 0;

int go(int v){
	if(in[v]) return 0;
	comp++;
	if(path[v].size() == 0) return 0;
	memset(a[v].p, -1, sizeof(a[v].p));
	a[v].d = 0;
	build(v, -1);
	
	mxdist = 0;
	mxid = v;
	dfs(v, -1, 0);
	mxdist = 0;
	v = mxid;
	dfs(v, -1, 0);
	int u = mxid;
	int o = lca(v, u);
	solo = max(solo, mxdist);
	int s = (mxdist + 1) >> 1;
	int q = 0;
	while(v != o){
		q += c[v][a[v].p[0]];
		if(q >= s){
			return min(q, mxdist - q + c[v][a[v].p[0]]);
		}
		v = a[v].p[0];
	}
	q = 0;
	while(u != o){
		q += c[u][a[u].p[0]];
		if(q >= s){
			return min(q, mxdist - q + c[u][a[u].p[0]]);
		}
		u = a[u].p[0];
	}
}

int travelTime(int N, int M, int L, int A[], int B[], int T[]) {
    
    for(int i = 0; i < M; i++){
    	path[A[i]].push_back(Path(B[i], T[i]));
    	path[B[i]].push_back(Path(A[i], T[i]));
    	c[A[i]][B[i]] = T[i];
    	c[B[i]][A[i]] = T[i];
	}
	int mx = 0;
	int mx2 = 0;
	int mx3 = 0;
	int s;
	for(int i = 0; i < N; i++){
		s = go(i);
		if(s > mx){
			mx3 = mx2;
			mx2 = mx;
			mx = s;
		} else if(s > mx2){
			mx3 = mx2;
			mx2 = s;
		} else {
			mx3 = max(mx3, s);
		}
	}
	if(comp == 1) return solo;
	if(comp == 2) return max(solo, L + mx + mx2);
	return max(L + mx + mx2, max(solo, mx3 + mx2 + L * 2));
}

Compilation message (stderr)

dreaming.cpp: In function 'int go(int)':
dreaming.cpp:106:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

• Subtask 1: 14 / 14
• Subtask 2: 10 / 10
• Subtask 3: 23 / 23
• Subtask 4: 18 / 18
• Subtask 5: 12 / 12
• Subtask 6: 23 / 23