Submission #134068

#	Time	Username	Problem	Language	Result	Execution time	Memory
134068		wilwxk	Tracks in the Snow (BOI13_tracks)	C++14	73.75 / 100	2120 ms	697540 KiB

tracks

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

const int MAXN=4e3+5;
const int MAXNN=16000005;
vector<int> g[MAXNN];
short cor[MAXNN];
short marc[MAXNN];
short ori[MAXN][MAXN];
char c[MAXN];
int rep[MAXNN], tam[MAXNN], dist[MAXNN];
vector<int> qu;
int dx[]={0, 1, 0, -1};
int dy[]={1, 0, -1, 0};
int n, m, respf;

int find(int cur) {
	if(rep[cur]==cur) return cur;
	return rep[cur]=find(rep[cur]);
}
void une(int a, int b) {
	a=find(a); b=find(b);
	if(a==b) return;
	if(tam[a]<tam[b]) swap(a, b);
	rep[a]=b;
}

void liga(int a, int b) {
	a=find(a); b=find(b);
	g[a].push_back(b);
	g[b].push_back(a);
	// printf("liga %d %d\n", a, b);
}

void bfs() {
	qu.push_back(find(0));
	dist[find(0)]=1;
	int ind=0;
	while(ind<qu.size()) {
		int cur=qu[ind++];
		cur=find(cur);
		if(marc[cur]==2) continue; marc[cur]=2; 
		respf=max(respf, dist[cur]);

		for(auto viz : g[cur]) {
			if(marc[find(viz)]!=0) continue;
			qu.push_back(find(viz));
			dist[viz]=dist[cur]+1;
			marc[find(viz)]=1;
		}
	}
}

int main() {
	scanf("%d %d", &n, &m);
	srand(time(0));
	for(int i=0; i<n; i++) for(int j=0; j<m; j++) rep[i*m+j]=tam[i*m+j]=i*m+j;
	random_shuffle(tam, tam+(n*m));

	for(int i=0; i<n; i++) {
		scanf(" %s", c);
		for(int j=0; j<m; j++) {
			if(c[j]=='.') ori[i][j]=0;
			else if(c[j]=='F') ori[i][j]=1;
			else ori[i][j]=2;
			cor[i*m+j]=ori[i][j];
		}
	}

	for(int i=0; i<n; i++) {
		for(int j=0; j<m; j++) {
			int cur=i*m+j;
			if(!cor[cur]) continue;
			for(int k=0; k<4; k++) {
				int ii=i+dx[k]; int jj=j+dy[k];
				if(ii<0||jj<0||ii>=n||jj>=m) continue;
				int viz=ii*m+jj;
				if(!cor[viz]) continue;

				if(ori[i][j]==ori[ii][jj]) une(cur, viz);
			}
		}
	}

	for(int i=0; i<n; i++) {
		for(int j=0; j<m; j++) {
			int cur=i*m+j;
			if(!cor[cur]) continue;
			for(int k=0; k<4; k++) {
				int ii=i+dx[k]; int jj=j+dy[k];
				if(ii<0||jj<0||ii>=n||jj>=m) continue;
				int viz=ii*m+jj;
				if(!cor[viz]) continue;

				if(cor[cur]!=cor[viz]) liga(cur, viz);
			}
		}
	}

	n*=m;
	bfs();

	printf("%d\n", respf);
}

Compilation message (stderr)

tracks.cpp: In function 'void bfs()':
tracks.cpp:39:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(ind<qu.size()) {
        ~~~^~~~~~~~~~
tracks.cpp:42:3: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   if(marc[cur]==2) continue; marc[cur]=2; 
   ^~
tracks.cpp:42:30: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
   if(marc[cur]==2) continue; marc[cur]=2; 
                              ^~~~
tracks.cpp: In function 'int main()':
tracks.cpp:55:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d", &n, &m);
  ~~~~~^~~~~~~~~~~~~~~~~
tracks.cpp:61:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf(" %s", c);
   ~~~~~^~~~~~~~~~

• Subtask 1: 30 / 30
• Subtask 2: 43.75 / 70