Here's my sol

public class Solution {

static void blast(char[][] grid,int i,int j,int[][] secPlanted){
    grid[i][j]='.';
    try{
        if(grid[i][j+1]=='O'&&secPlanted[i][j+1]==3){
            blast(grid,i,j+1,secPlanted);
        }
        grid[i][j+1]='.';
        secPlanted[i][j+1]=0;
    }catch(ArrayIndexOutOfBoundsException e){}
    try{
        if(grid[i][j-1]=='O'&&secPlanted[i][j-1]==3){
            blast(grid,i,j-1,secPlanted);
        }
        grid[i][j-1]='.';
        secPlanted[i][j-1]=0;
    }catch(ArrayIndexOutOfBoundsException e){}
    try{
        if(grid[i-1][j]=='O'&&secPlanted[i-1][j]==3){
            blast(grid,i-1,j,secPlanted);
        }
        grid[i-1][j]='.';
        secPlanted[i-1][j]=0;
    }catch(ArrayIndexOutOfBoundsException e){}
    try{
        if(grid[i+1][j]=='O'&&secPlanted[i+1][j]==3){
            blast(grid,i+1,j,secPlanted);
        }
        grid[i+1][j]='.';
        secPlanted[i+1][j]=0;
    }catch(ArrayIndexOutOfBoundsException e){}
}

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int r=sc.nextInt(),c=sc.nextInt(),n=sc.nextInt();
    String[] gridString = new String[r];
    int sec=0;
    char[][] grid = new char[r][c];
    for(int i=0;i<r;i++){
        gridString[i]=sc.next();
        grid[i]=gridString[i].toCharArray();
    }
    sec++;//1 sec
    sec++;//2 secs
    int[][] secPlanted = new int[r][c];
    for(int i=0;i<r;i++){
        for(int j=0;j<c;j++){
            secPlanted[i][j] = grid[i][j]=='O'?2:0; 
        }
    }
    while(sec<=n){
        while(n-sec>4)
            sec+=4;
        //fill empty places
        if(sec%2==0){
            for(int i=0;i<r;i++)
                for(int j=0;j<c;j++)
                    if(grid[i][j]=='.')
                        grid[i][j]='O';
        }

        //bomb blast
        if(sec%2==1){
            for(int i=0;i<r;i++){
                for(int j=0;j<c;j++){
                    if(secPlanted[i][j]==3){
                        secPlanted[i][j]=0;
                        blast(grid,i,j,secPlanted);
                    }
                }
            }
        }
        for(int i=0;i<r;i++)
            for(int j=0;j<c;j++)
                secPlanted[i][j] = grid[i][j]=='O' ? secPlanted[i][j]+1 : 0;
        sec++;

    }

    //final grid
    for(int i=0;i<r;i++){
        for(int j=0;j<c;j++)
            System.out.print(grid[i][j]);
        System.out.println();
    }
}

}