Submission #1063720

#	Time	Username	Problem	Language	Result	Execution time	Memory
1063720		danielzhu	Tracks in the Snow (BOI13_tracks)	C++17	95.63 / 100	1957 ms	1048576 KiB

tracks

#include <bits/stdc++.h>
using namespace std;
int H, W;
int grid[4001][4001], cc[4001][4001];
queue<pair<int,int>> q;
vector<pair<int,int>> dir = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
 
void ff(int cur, int val){
	while(!q.empty()){
		auto temp = q.front();
		int x = temp.first, y = temp.second;
		q.pop();
		for(auto [dx, dy] : dir){
			if((x+dx > -1)&& (x+dx < H) && (y+dy > -1) && (y+dy < W) && (cc[x+dx][y+dy] == -1) && (grid[x+dx][y+dy] == cur)){
				cc[x+dx][y+dy] = val;
				q.push({x+dx, y+dy});
			}
		}
	}
}				
 
int main(){
	cin>>H>>W;
	memset(grid, 0, sizeof(grid));
	memset(cc, -1, sizeof(cc));
	for(int i = 0; i < H; i++){
		string s; cin>>s;
		for(int j = 0; j < W; j++){
			if(s[j] == 'F') grid[i][j] = 1;
			else if(s[j] == 'R') grid[i][j] = 2;
		}
	}
	int val = 0;
	for(int i = 0; i < H; i++){
		for(int j = 0; j < W; j++){
			if(cc[i][j] == -1 && grid[i][j] != 0){
				cc[i][j] = val;
				q.push({i,j});
				ff(grid[i][j], val);
				val++;
			}
		}
	}
	vector<unordered_set<int>> adj(val+1); 
	for(int i = 0; i < H; i++){
		for(int j = 0; j < W; j++){
			if(grid[i][j] != 0){
				for(auto [dx, dy] : dir){
					if(i+dx > -1 && i+dx < H && j+dy > -1 && j+dy < W && grid[i+dx][j+dy] != grid[i][j] && grid[i+dx][j+dy] != 0){
						adj[cc[i][j]].insert(cc[i+dx][j+dy]);
						adj[cc[i+dx][j+dy]].insert(cc[i][j]);
					}
				}
			}
		}
	}
	queue<int> q1;
	q1.push(0);
	vector<int> v(val+1, 0), d(val+1, 0);
	v[0] = 1;
	int ans = 0;
	while(!q1.empty()){
		auto temp = q1.front();
		q1.pop();
		for(auto i : adj[temp]){
			if(!v[i]){
				q1.push(i);
				v[i] = 1;
				d[i] = d[temp] + 1;
				ans = max(ans, d[i]);
			}
		}
	}
	cout<<ans+1<<endl;
	return 0;
}

• Subtask 1: 30 / 30
• Subtask 2: 65.625 / 70