Submission #1249437

#	Time	Username	Problem	Language	Result	Execution time	Memory
1249437		Joseph0121	Race (IOI11_race)	C++20	100 / 100	315 ms	63584 KiB

race

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

const int maxn = 2e5+5;

vector<pair<int,int>> e[maxn];
int sz[maxn], heavy[maxn], par[maxn], heavy_par[maxn];
map<int,int> mp;
int ans = 1e9;
void dfs1(int node, int parent){
	int heavy_child = -1, sz_child = -1;
	for(auto i: e[node]){
		if(i.first == parent) continue;
		par[i.first] = node;
		dfs1(i.first,node);
		if(sz[i.first] > sz_child){
			heavy_child = i.first;
			sz_child = sz[i.first];
		}
		sz[node]+=sz[i.first];
	}
	sz[node]+=1;
	heavy[node] = heavy_child;
	heavy_par[heavy_child] = node;
}
void dfs3(int node, int parent, int dist_now, int depth, vector<array<int,2>> &node_dist, int K){
	node_dist.push_back({dist_now, depth});
	if(dist_now > K) return;
	for(auto i: e[node]){
		if(i.first == parent) continue;
		dfs3(i.first, node, dist_now+i.second, depth+1, node_dist, K);
	}
}
array<int,2> dfs2(int node, int parent, int K){
	//go down the heavy child first
	if(heavy[node] == -1) return {0,0};
	
	//first return = total weight added, second return = total edges added
	array<int,2> tmp = dfs2(heavy[node],node,K);
	int add_weight = tmp[0], add_edge = tmp[1];
	
	add_edge++;
	for(auto i: e[node]){
		if(i.first == heavy[node]){
			add_weight+=i.second;
			break;
		}
	}
	mp[-add_weight] = -add_edge;

	if(mp.count(K-add_weight) != 0){
		ans = min(ans,mp[K-add_weight]+add_edge);
	}
	
	vector<array<int,2>> node_dist;
	for(auto i: e[node]){
		if(i.first!=parent && i.first!=heavy[node]){
			
			dfs3(i.first, node, i.second, 1, node_dist, K); //now I have all the distances
			
			for(auto j: node_dist){
				//j[0] = distance, j[1] = minimum edges to cover
				if(mp.count(K-add_weight-j[0]) != 0){
					ans = min(ans,mp[K-add_weight-j[0]]+j[1]+add_edge);
				}
			}		
			//add everything in
			for(auto j: node_dist){
				if(mp.count(j[0]-add_weight) != 0){
					 mp[j[0]-add_weight] = min(mp[j[0]-add_weight], j[1]-add_edge);
				}
				else mp[j[0]-add_weight] = j[1]-add_edge;
			}
			node_dist.clear();
		}
	}
	return {add_weight, add_edge};
}



int best_path(int N, int K, int H[][2], int L[]){
	for(int i = 0;i<N;i++){
		 par[i] = -1;
		 heavy_par[i] = -1;
	}
	
 	for(int i = 0;i<N-1;i++){
		e[H[i][0]].push_back(make_pair(H[i][1],L[i]));
		e[H[i][1]].push_back(make_pair(H[i][0],L[i]));
	}
	dfs1(0,0); 

	for(int i = 0;i<N;i++){
		if(heavy_par[i] == -1){
			//it's top of a chain
			mp[0] = 0;
			dfs2(i,par[i],K);
			mp.clear();
		}
	}
	
	if(ans == 1e9) return -1;
	else return ans;
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 57 / 57