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| #include <stdio.h>
#include <queue>
#include <memory.h>
using namespace std;
int R, C, maxday;
int lake[1500][1500];
bool visit[1500][1500];
int dx[4] = {0,1,0,-1};
int dy[4] = {-1,0,1,0};
int Dpos[2];
void INIT(){
maxday = 0;
queue<pair<int,int>> ice;
char buf[1500][1501];
for(int i = 0; i < R; ++i)
scanf("%s",buf[i]);
for(int i = 0; i < R; ++i)
for(int j = 0; j < C; ++j) {
if(buf[i][j]=='L'||buf[i][j]=='.'){
if(buf[i][j]=='L') lake[i][j] = -1,Dpos[0] = i, Dpos[1] = j;
for(int k = 0; k < 4; ++k){
int nx = j+dx[k];
int ny = i+dy[k];
if(0<=nx&&nx<C && 0<=ny&&ny<R && buf[ny][nx]=='X' && !lake[ny][nx]){
lake[ny][nx] = 1;
ice.emplace(ny,nx);
}
}
}
else continue;
}
while(!ice.empty()){
int x = ice.front().second;
int y = ice.front().first;
maxday = max(maxday,lake[y][x]);
ice.pop();
for(int i = 0; i < 4; ++i){
int nx = x + dx[i];
int ny = y + dy[i];
if(0<=nx&&nx<C && 0<=ny&&ny<R && buf[ny][nx]=='X' && !lake[ny][nx]){
lake[ny][nx] = lake[y][x] + 1;
ice.emplace(ny,nx);
}
}
}
}
bool BFS(int day){
queue<pair<int, int>> duck;
memset(visit,false,sizeof(visit));
duck.emplace(Dpos[0],Dpos[1]);
visit[Dpos[0]][Dpos[1]] = true;
while(!duck.empty()){
int x = duck.front().second;
int y = duck.front().first;
duck.pop();
for(int i = 0; i < 4; ++i){
int nx = x + dx[i];
int ny = y + dy[i];
if(0<=nx&&nx<C && 0<=ny&&ny<R && !visit[ny][nx] && lake[ny][nx]<=day){
if(lake[ny][nx] == -1) return true;
visit[ny][nx] = true;
duck.emplace(ny,nx);
}
}
}
return false;
}
int binary_search_BFS(){
int l = 0, r = maxday;
while(l+1<r) BFS((l+r)>>1) ? r = (l+r)>>1 : l = (l+r)>>1;
return BFS(l) ? l : r;
}
int main(){
scanf("%d %d",&R,&C);
INIT();
printf("%d",binary_search_BFS());
}
|
