I inserted syntax to add and initialize global variables. These globals are only initialized the first time the script is executed or when the reset_globals; keyword is called. In this way data can be shared over a series of script executions. I decided to test out some of the language features by solving that pesky 8 queens problem. I used a single array of integers to store queen positions and three other arrays to assess the threat level of a particular square.
Here is the A2 source:
// Global variables can be used to share data with all functions// The globals can are only initialized the first time a script// is called. The reset_global; keyword can be used at any time// to re-initialize global variables.global{ int Queens[8;] = {0;0;0;0;0;0;0;0;}; int RowAttack[8;] = {0;0;0;0;0;0;0;0;}; int NegDiagAttack[15;] = {0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;}; int PosDiagAttack[15;] = {0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;};}// This is the entry point of the script// It resets the global variables and then runs the // 8 queens function. After that the values of the// each queen are printed.function void main(void){ // Reset globals reset_global; // Solve the 8 queens Do_8_Queens(0;); // Print the solution print "Columns:"; print "0 1 2 3 4 5 6 7"; print "Rows:"; print Queens; }// This function sets a queen to the global Queens array.// It also sets the attack arrays which are used in the // Is_Under_Attack() function.function void Set_Queen(int Column, int Row){ // Set the queens array Queens[Column;] = Row; // Set the RowAttack array RowAttack[Row;] = 1; // Set the Negatice Diagnal Attack NegDiagAttack[(Column - Row)+7;] = 1; // Set the Positive Diagnal Attack PosDiagAttack[Column + Row;] = 1;}// This function removes a queen from the global Queens // array. It also removes the attack array values which // are used in the Is_Under_Attack() function.function void Remove_Queen(int Column, int Row){ // Set the queens array Queens[Column;] = 0; // Set the RowAttack array RowAttack[Row;] = 0; // Set the Negative Diagnal Attack NegDiagAttack[(Column - Row)+7;] = 0; // Set the Positive Diagnal Attack PosDiagAttack[Column + Row;] = 0;}// Determines if a given square is under attack from// another queen. Returns a 1 if the square is under// attack and a 0 if not.function int Is_Under_Attack(int Column, int Row){ // Check row attack if(RowAttack[Row;] == 1) { return 1; } // Check negative diagnal attack if(NegDiagAttack[(Column - Row)+7;] == 1) { return 1; } // Check positive diagnal attack if(PosDiagAttack[Column + Row;] == 1) { return 1; } return 0;}// This function calculates the 8 queen positions// and stores them in the Queens array in the form// Queens[Column_Index] = Row_Index. It uses// recursion and backtracking to solve the problem.// The function must be called with a zero value// and therefore only solves the 8 queens for a single// case when the first queen is in column = 0, row = 0.function int Do_8_Queens(int Column){ // If we surpass 7 columns then we have succeeded if(Column > 7) { return 1; } else // We are still looking for a solution { int Row = 0; int Done = 0; // Loop while not done and still working on rows while((Done == 0) & (Row <= 7)) { // Check to see if the current square is under attack if(Is_Under_Attack(Column; Row;) == 1) { // If so then increment the row Row = Row + 1; } else // The square is safe so { // Place a queen in that square Set_Queen(Column; Row;); // Move on to the next column Done = Do_8_Queens(Column+1;); // If we have not succeeded then if(Done == 0) { // Remove the queen (backtrack) Remove_Queen(Column; Row;); // And increment the current row Row = Row + 1; } else // Success { return 1; } } } } return 0;}The output looks like this:
Columns:
0 1 2 3 4 5 6 7
Rows:
0 4 7 5 2 6 1 3
