Question

Here’s the link to the problem: http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=13&page=show_problem&problem=1130

This is my code and it works perfectly; however, it gives wrong answer whenever I submit it. Does anybody know why?

NOTE: I pad the matrix with 2 extra rows and columns so that when I’m checking the left of the first column or the bottom of the last row, I don’t get an error.

//A minesweeper generator
#include <iostream>
#include <sstream>

using namespace std;

char arr[102][102]; //2D dynamic array used temporarily

int main() {
    int n, m; //Rows and columns
    int count = 0, recordNum = 0; //Number of mines around the current dot

    while(true) { //Keep processing records until "0 0" is encountered
        cin >> n >> m;

        if(n == 0 && m == 0 ) //End of input
            break;

        //Read the values into the array
        for(int i = 1; i < n+1; i++) { //Rows
            for(int j = 1; j < m+1; j++) { //Columns
                cin >> arr[i][j];
            }
        }

        //Process the values of the array and generate the numbers
        for(int i = 1; i < n+1; i++) { //Rows
            for(int j = 1; j < m+1; j++) { //Columns
                if(arr[i][j] == '*')
                    continue;
                else { //Count the number of mines around this dot
                    if(arr[i-1][j-1] == '*')
                                        count++;
                                    if(arr[i-1][j] == '*')
                                        count++;
                                    if(arr[i-1][j+1] == '*')
                        count++;
                    if(arr[i][j-1] == '*')
                                        count++;
                                    if(arr[i][j+1] == '*')
                                        count++;
                                    if(arr[i+1][j-1] == '*')
                        count++;
                    if(arr[i+1][j] == '*')
                                        count++;
                                    if(arr[i+1][j+1] == '*')
                        count++;
                }

                //Create a buffer to convert the count to a char
                stringstream buffer;
                buffer << count;
                arr[i][j] = buffer.str().at(0);

                count = 0; //Finally reset the counter
            }
        }

        if(recordNum > 0)
            cout << endl;
        recordNum++;
        cout << "Field #" << recordNum << ":\n";

        //Output the values
        for(int i = 1; i < n+1; i++) { //Rows
            for(int j = 1; j < m+1; j++) { //Columns
                cout << arr[i][j];
            }
            cout << endl;
        }
    }
    return 0;
}

Answer 1

No attempt is made to clear out arr[][] between runs (or clear at start), so a 4×4 minefield with a * in the 4th position will cause a next 3×3 minefield to have incorrect values.