BFS_GRID.java

//pakage joney_000[let_me_start]
//
import java.util.*;
import java.lang.*;
import java.io.*;
import java.math.*;
/*
 * Author    : joney_000[let_me_start]
 * Algorithm : BinarySearch UpperBound & Lower Bound
 * Platform  : N/A
 *
 */
public class A {

  private InputStream inputStream ;
  private OutputStream outputStream ;
  private FastReader in ;
  private PrintWriter out ;
  /*
    Overhead [Additional Temporary Strorage] but provides memory reusibility for multiple test cases.
    Size Limit : 10^5 + 4 
  */
  private final int BUFFER = 10005;
  private int    tempints[] = new int[BUFFER];
  private long   templongs[] = new long[BUFFER];
  private double tempdoubles[] = new double[BUFFER];
  private char   tempchars[] = new char[BUFFER];
  private final long mod = 1000000000+7;
  private final int  INF  = Integer.MAX_VALUE / 10;
  private final long INF_L  = Long.MAX_VALUE / 10;

  public A(){}
  public A(boolean stdIO)throws FileNotFoundException{
    // stdIO = false;
    if(stdIO){
      inputStream = System.in;
      outputStream = System.out;
    }else{
      inputStream = new FileInputStream("output.txt");
      outputStream = new FileOutputStream("output1.txt");
    }
    in = new FastReader(inputStream);
    out = new PrintWriter(outputStream);

  }
	int n, m, q;
	// 8 Dir
	// int dx[] = {-1 ,-1 , -1 , 0 , 0, 1 ,1 ,1};
	// int dy[] = {-1 , 0 ,  1 ,-1 , 1,-1 ,0 ,1};
	// 4 Dir
	int dx[] = {-1, 1, 0, 0};
	int dy[] = { 0, 0, 1, -1};

	int cnt[][] = new int[1005][1005];

  void run()throws Exception{
    // int tests = i();
    // for(int t = 1 ; t <= tests; t++){
      n = i(); m = i(); q = i();
      clear();
      for(int i = 1; i <= n; i++){
      	for(int j = 1; j <= m; j++){
      		char ch = c();
      		mat[i][j] = ch;
      	}
      }
      for(int i = 1; i <= n; i++){
      	for(int j = 1; j <= m; j++){
      		if(mat[i][j] == '.' && !vis[i][j])bfs(i, j);
      	}
      }
      for(int i = 1; i <= q; i++){
      	out.write(""+cnt[i()][i()]+"\n");
      }
      
    // }
  }// end run

  boolean vis[][] = new boolean[1005][1005];
  char mat[][] = new char[1005][1005];
  
  void clear(){

  }

	boolean isValid(int i , int j){
	 	if(i <= n && i >= 1 && j <= m && j>= 1 && (!vis[i][j]))return true;
	 	else return false;
	}

	void bfs(int xroot, int yroot){

	  LinkedList <Integer> xq = new LinkedList<Integer>();
	  LinkedList <Integer> yq = new LinkedList<Integer>();

	  // int l = 0;//level and will be marked at the time of adding into queue
	  LinkedList<Integer> level_q = new LinkedList<Integer>();
	  xq.add(xroot);
	  yq.add(yroot);
	  vis[xroot][yroot] = true;
	  //level[root] = 0;
	  level_q.add(0);

	  while(!xq.isEmpty()){
	  
      int ux = xq.removeFirst(); //first
      int uy = yq.removeFirst(); //first
     	// l = level_q.removeFirst();
	    //level[u] = l;		
      for(int i = 0 ; i <= 3 ; i++){
        int vx = ux + dx[i] ;
        int vy = uy + dy[i];	
        if(isValid(vx ,vy) && mat[vx][vy] == '.'){
            vis[vx][vy] = true;
            xq.add(vx); yq.add(vy);

            // level_q.add(l+1);
        		// f[v] = u;
        		// level[v] = l+1;
        }
      }
	  }
	
  }
  
  long gcd(long a , long b){
    if(b==0)return a;
    return gcd(b , a%b);
  }

  long lcm(long a , long b){
    if(a==0||b==0)return 0;
    return (a*b)/gcd(a,b);
  }

  long mulmod(long a , long b ,long mod){
    if(a==0||b==0)return 0;
    if(b==1)return a;
    long ans = mulmod(a,b/2,mod);
    ans = (ans*2)% mod;
    if(b%2==1)ans = (a + ans)% mod;
    return ans;
  }
  
  long pow(long a , long b ,long mod){
    if(b==0)return 1;
    if(b==1)return a;
    long ans = pow(a,b/2,mod);
    ans = (ans * ans);
    if(ans >= mod )ans %= mod;

    if(b%2==1)ans = (a * ans);
    if(ans >= mod )ans %= mod;

    return ans;
  }
  // 20*20   nCr Pascal Table
  long[][] ncrTable(){
    long ncr[][] = new long[21][21];
    for(int i=0 ;i<=20 ;i++){ncr[i][0]=1;ncr[i][i]=1;}
      for(int j=0;j<=20 ;j++){
        for(int i=j+1;i<= 20 ;i++){
          ncr[i][j] = ncr[i-1][j]+ncr[i-1][j-1];
        }
      }
    return ncr;
  }
  //*******************************I/O******************************//  
  int i()throws Exception{
    //return Integer.parseInt(br.readLine().trim());
    return in.nextInt();
  }
  int[] is(int n)throws Exception{
  //int arr[] = new int[n+1];
    for(int i=1 ; i <= n ;i++)tempints[i] = in.nextInt();  
      return tempints;
  }
  long l()throws Exception{
    return in.nextLong();
  }
  long[] ls(int n)throws Exception{
    for(int i=1 ; i <= n ;i++)templongs[i] = in.nextLong();  
      return templongs;
  }

  double d()throws Exception{
    return in.nextDouble();
  }
  double[] ds(int n)throws Exception{
    for(int i=1 ; i <= n ;i++)tempdoubles[i] = in.nextDouble();  
      return tempdoubles;
  }
  char c()throws Exception{
    return in.nextCharacter();
  }
  char[] cs(int n)throws Exception{
    for(int i=1 ; i <= n ;i++)tempchars[i] = in.nextCharacter();  
      return tempchars;
  }
  String s()throws Exception{
    return in.nextLine();
  }
  BigInteger bi()throws Exception{
    return in.nextBigInteger();
  }
//***********************I/O ENDS ***********************//
//*********************** 0.3%f [precision]***********************//
/* roundoff upto 2 digits 
   double roundOff = Math.round(a * 100.0) / 100.0;
                    or
   System.out.printf("%.2f", val);
          
*/
/*
  print upto 2 digits after decimal
  val = ((long)(val * 100.0))/100.0;
  
*/    

    private void closeResources(){
     out.flush();
     out.close();
     return;
    }
    public static void main(String[] args) throws java.lang.Exception{
    //let_me_start Shinch Returns 


    /*  
        // Old Reader Writer
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter out=new BufferedWriter(new OutputStreamWriter(System.out));
    BufferedReader br=new BufferedReader(new FileReader("input.txt"));
        BufferedWriter out=new BufferedWriter(new FileWriter("output.txt"));
    */   
        A driver = new A(true);
        
        driver.run();

        driver.closeResources();
        return ;

      }  

    }

    class FastReader{

      private boolean finished = false;

      private InputStream stream;
      private byte[] buf = new byte[4 * 1024];
      private int curChar;
      private int numChars;
      private SpaceCharFilter filter;

      public FastReader(InputStream stream){
        this.stream = stream;
      }

      public int read(){
        if (numChars == -1){
          throw new InputMismatchException ();
        }
        if (curChar >= numChars){
          curChar = 0;
          try{
            numChars = stream.read (buf);
          } catch (IOException e){
            throw new InputMismatchException ();
          }
          if (numChars <= 0){
            return -1;
          }
        }
        return buf[curChar++];
      }

      public int peek(){
        if (numChars == -1){
          return -1;
        }
        if (curChar >= numChars){
          curChar = 0;
          try{
            numChars = stream.read (buf);
          } catch (IOException e){
            return -1;
          }
          if (numChars <= 0){
            return -1;
          }
        }
        return buf[curChar];
      }

      public int nextInt(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        int sgn = 1;
        if (c == '-'){
          sgn = -1;
          c = read ();
        }
        int res = 0;
        do{
          if(c==','){
            c = read();
          }
          if (c < '0' || c > '9'){
            throw new InputMismatchException ();
          }
          res *= 10;
          res += c - '0';
          c = read ();
        } while (!isSpaceChar (c));
        return res * sgn;
      }

      public long nextLong(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        int sgn = 1;
        if (c == '-'){
          sgn = -1;
          c = read ();
        }
        long res = 0;
        do{
          if (c < '0' || c > '9'){
            throw new InputMismatchException ();
          }
          res *= 10;
          res += c - '0';
          c = read ();
        } while (!isSpaceChar (c));
        return res * sgn;
      }

      public String nextString(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        StringBuilder res = new StringBuilder ();
        do{
          res.appendCodePoint (c);
          c = read ();
        } while (!isSpaceChar (c));
        return res.toString ();
      }

      public boolean isSpaceChar(int c){
        if (filter != null){
          return filter.isSpaceChar (c);
        }
        return isWhitespace (c);
      }

      public static boolean isWhitespace(int c){
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
      }

      private String readLine0(){
        StringBuilder buf = new StringBuilder ();
        int c = read ();
        while (c != '\n' && c != -1){
          if (c != '\r'){
            buf.appendCodePoint (c);
          }
          c = read ();
        }
        return buf.toString ();
      }

      public String nextLine(){
        String s = readLine0 ();
        while (s.trim ().length () == 0)
          s = readLine0 ();
        return s;
      }

      public String nextLine(boolean ignoreEmptyLines){
        if (ignoreEmptyLines){
          return nextLine ();
        }else{
          return readLine0 ();
        }
      }

      public BigInteger nextBigInteger(){
        try{
          return new BigInteger (nextString ());
        } catch (NumberFormatException e){
          throw new InputMismatchException ();
        }
      }

      public char nextCharacter(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        return (char) c;
      }

      public double nextDouble(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        int sgn = 1;
        if (c == '-'){
          sgn = -1;
          c = read ();
        }
        double res = 0;
        while (!isSpaceChar (c) && c != '.'){
          if (c == 'e' || c == 'E'){
            return res * Math.pow (10, nextInt ());
          }
          if (c < '0' || c > '9'){
            throw new InputMismatchException ();
          }
          res *= 10;
          res += c - '0';
          c = read ();
        }
        if (c == '.'){
          c = read ();
          double m = 1;
          while (!isSpaceChar (c)){
            if (c == 'e' || c == 'E'){
              return res * Math.pow (10, nextInt ());
            }
            if (c < '0' || c > '9'){
              throw new InputMismatchException ();
            }
            m /= 10;
            res += (c - '0') * m;
            c = read ();
          }
        }
        return res * sgn;
      }

      public boolean isExhausted(){
        int value;
        while (isSpaceChar (value = peek ()) && value != -1)
          read ();
        return value == -1;
      }

      public String next(){
        return nextString ();
      }

      public SpaceCharFilter getFilter(){
        return filter;
      }

      public void setFilter(SpaceCharFilter filter){
        this.filter = filter;
      }

      public interface SpaceCharFilter{
        public boolean isSpaceChar(int ch);
      }
    }
    /******************** Pair class ***********************/

  class Pair implements Comparable<Pair>{
     public int a;
     public int b;
     public Pair(){
      this.a = 0;
      this.b = 0;
    }
    public Pair(int a,int b){
      this.a = a;
      this.b = b;
    }
    public int compareTo(Pair p){
      if(this.b==p.b){
       return this.a-p.a;  
     }
     return (this.b - p.b); 
   }
   public String toString(){
    return "a="+this.a+" b="+this.b;
  }

}