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n-Queens problem implemented in C
Posted Date:
Total Responses: 0
Posted By: Pratik Pansare Member Level: Gold Points/Cash: 5
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#include
#include
char board[48][48],row=0;
unsigned n;
void main()
{
char i,j;
for(clrscr(),printf("Enter the no. of squares.\n");;printf("Max. capacity is 48 X 48 board.\n"))
if(scanf("%d",&n),n<49) // obtaining and validating input
break;
for(i=0;i for(j=0;j board[i][j]=0;
if(queens()) // calling main logic
printf("Not all possibilities have been shown.\n");
else
printf("That's it.\n");
if(!getch())
getch();
}
queens() // recursive function implementing backtracking
{
char col,i;
if(row-n) // if last row hasn't been filled
{
for(col=0;col if(!board[row][col]) // if current square is not attacked by any queen
{
for(i=0;i {
board[row][i]++,board[i][col]++; // row, column
if(row+i>=col&&row+i board[row-col+i][i]++;
if(row+col>=i&&row+col board[row+col-i][i]++;
}
if(board[row++][col]=-1,queens()) // RECURSIVELY CALL for filling next row after marking current square as occupied
return 1; // exit recursively to main if ESC is pressed to prevent further calculations
for(row--,i=0;i { // do the exact reverse process, i.e., decrementing squares under attack
board[row][i]--,board[i][col]--; // row, column
if(row+i>=col&&row+i board[row-col+i][i]--;
if(row+col>=i&&row+col board[row+col-i][i]--;
}
board[row][col]=0; // change -1 to 0 as only if it was 0 would it have entered if(!board[row][col])
}
return 0;
}
else // if last row has been filled, success! a solution has been found
{
if(n<25) // if n is small, print large output with grid lines
{
for(row=0;row {
for(col=0;col printf("+-");
for(printf("+\n"),col=0;col if(board[row][col]+1)
printf("| ");
else
printf("|Q");
}
for(i=0;i printf("+-");
printf("+\n");
}
else // otherwise print without grid lines
for(row=0;row for(col=0;col if(board[row][col]+1)
putchar(' ');
else
putchar('Q');
if(getch()-27)
printf("Please wait....\n");
else
return 1;
return 0;
}
}
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