Why does my Actionscript 3 program randomly get stuck in an infinite loop?

Question

mBlocks is a 2-dimensional array of Block objects. Every time my application runs, it runs the InitGridNumbers function. Sometimes, it will get stuck in an infinite loop. Other times, it builds and runs without issues.

  public function InitGridNumbers():void
  {
   var tempRow:Array;
   var tempColumn:Array;
   var tempNum:int;
   for (var i:int = 0; i < mNumRows; i++)
   {
    tempRow = GetRow(i);
    for (var j:int = 0; j < mNumColumns; j++)
    {
     // if number is unassigned
     if (tempRow[j] == 0)
     {
      var cantMoveOn:Boolean = true;
      while (cantMoveOn)
      {
       tempNum = Math.random() * mNumColumns + 1;
       if (!CheckRow(i, tempNum) && !CheckColumn(j, tempNum))
        cantMoveOn = false;
      }
      mBlocks[i][j].SetNumber(tempNum);     
     }
    }
   }
  } 

---

  public function CheckRow(rowNum:int, checkNum:int):Boolean
  {
   var tempRow:Array = GetRow(rowNum);
   for (var i:int = 0; i < mNumColumns; i++)
   {
    if (checkNum == tempRow[i])
     return true;
   }
   return false;
  }

  public function CheckColumn(columnNum:int, checkNum:int):Boolean
  {
   var tempColumn:Array = GetColumn(columnNum);
   for (var i:int = 0; i < mNumColumns; i++)
   {
    if (checkNum == tempColumn[i])
     return true;
   }
   return false;
  }

---

  public function GetRow(rowNum:int):Array
  {
   var rowArray:Array = new Array(mNumRows);
   for (var i:int = 0; i < mNumRows; i++)
    rowArray[i] = mBlocks[rowNum][i].mNumber;

   return rowArray;
  }

  public function GetColumn(columnNum:int):Array
  {
   var columnArray:Array = new Array(mNumColumns);
   for (var i:int = 0; i < mNumColumns; i++)
    columnArray[i] = mBlocks[i][columnNum].mNumber;
   return columnArray;
  }

Answer 1

To begin with, checkColumn, getColumn and getRow methods are wrong. To get a row, you should copy numColumns items and to get a column, you should copy numRows items. In other words, if there are r rows and c columns, there would be c items per each row and r items per each column.

public function checkColumn(columnNum:int, checkNum:int):Boolean
{
  var tempColumn:Array = getColumn(columnNum);
  for (var i:int = 0; i < mNumRows; i++)
  {
    if (checkNum == tempColumn[i])
      return true;
  }
  return false;
}

public function getRow(rowNum:int):Array
{
  var rowArray:Array = new Array();//needn't specify length in advance.
  for (var i:int = 0; i < mNumColumns; i++)
    rowArray[i] = mBlocks[rowNum][i].mNumber;

  return rowArray;
}
public function getColumn(columnNum:int):Array
{
  var columnArray:Array = new Array();
  for (var i:int = 0; i < mNumRows; i++)
    columnArray[i] = mBlocks[i][columnNum].mNumber;
  return columnArray;
}

---

while (cantMoveOn)
{
  //call Math.floor
  tempNum = Math.floor(Math.random() * mNumColumns) + 1;
  if (!checkRow(i, tempNum) && !checkColumn(j, tempNum))
    cantMoveOn = false;
}

It looks like you're checking for a number that is not present in the current row and column. It's hard to say without knowing more details, but can you think of a scenario where this would be impossible?

For example, if there are four columns and five rows, the tempNum would always be between one and four. Now if the number of rows is five and the corresponding column already has all numbers up to four, the if statement would never evaluate to true and hence you'd end up in an infinite loop

0 1 2 3
1
2
3
4

---

in case grid is a square, how about this:

0 1 2 3
4
0
0