C Program to Solve Tower of Hanoi Puzzle

This is a c program to solve towers of Hanoi puzzle problem. This simple c program give solution for tower of Hanoi problem with any number of disks. Tower of Hanoi is a mathematical game or puzzle. It is also called tower of Brahma or Lucas' tower. There are three towers (or rods) and a number of disks of different diameters. Initially, The disks have hole at center so that it can slide on to the rods. initially all disks are stacked on the first tower, say tower A, such that no disk is placed over a smaller disk. The goal or objective is to move all these disks from tower A (first tower) to tower C (third tower). But you should obey the following rules. The rules of towers of Hanoi puzzle are:

C Program to Validate Sudoku - Checking Correctness of Sudoku

Here we shall see a c program to validate sudoku a sudoku. The c program i have written here checks the correctness of a sudoku. The programs can be used to check sudoku solution for 9x9 sudoku. First of all, we should know what are the constraints.

• Each row should contain all numbers from 1 to 9 (inclusive)
• Each column should contain all numbers from 1 to 9 (inclusive)
• The 3x3 squares should also contain all numbers from 1 to 9 (inclusive)

If all above conditions are satisfied, the sudoku is correct. The c program to check whether a solution for a sudoku is correct is as follows:

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>

void report(char *s,int i,int j)
{
printf("\nThe sudoku is INCORRECT");
printf("\nin %s. Row:%d,Column:%d",s,i+1,j+1);
getch();
exit(0);
}

void main()
{
int i,j,a[9][9];
char c;
int si,sj,flag;
printf("\nEnter the sudoku");
/*
Going to read sudoku matrix (9x9).
Since numbers 1 to 9 are single digit,
it is enough to read them as char.
To convert them from their ascii to int,
subtract ascii of '0' from the character.
*/
for(i=0;i<9;i++)
    for(j=0;j<9;j++)
    {
    scanf("%c",&c);
    a[i][j]=c-'0';
    }
/*++++++++++++++++++
checking rows
+++++++++++++++++++
we check each cell in each row.
We start with a flag 0x0000.
if 1 is found zeroth bit of flag is set.
if 2 is found, first bit is set
and so on.
If all digits 1 to 9 are present, flag's value
will be 0x01FF.
If flag is 0x01FF after traversing a row,
the row has all numbers 1 to 9.
So, it is correct.
If the flag is not 0x01FF after traversing a row,
the row is incorrectly filled.
Then we call report() function
*/
for(i=0;i<9;i++)
    {
    flag=0x0000;
    for(j=0;j<9;j++)
        flag|=1<<(a[i][j]-1);
    if(flag!=0x01FF)
        report("row",i,j-1);
    }

/*++++++++++++++++++
checking columns
+++++++++++++++++++
Just like row checking.
The flag is for a column.
*/
for(j=0;j<9;j++)
    {
    flag=0x0000;
    for(i=0;i<9;i++)
        flag|=1<<(a[i][j]-1);
    if(flag!=0x01FF)
        report("col",i-1,j);
    }
/*++++++++++++++++++
checking Squares (3x3)
+++++++++++++++++++
Just like row checking.
The flag is for a square.
*/
for(si=0;si<3;si++)
    {
    for(sj=0;sj<3;sj++)
        {
        flag=0x0000;
        for(i=0;i<3;i++)
            {
            for(j=0;j<3;j++)
                flag|=1<<(a[si*3+i][sj*3+j]-1);

            }
        if(flag!=0x01FF)
                report("square",si*3+i-1,sj*3+j-1);
        }
    }
printf("\nThe sudoku is correct");
}

To test the program, you may try the following inputs. You may copy paste a line from below sudoku solutions to the program. (Each line is a correct solution)

123456789759183426648297315374915268896372154512864973931528647265749831487631592
123456789857923164964817235386241597275639841491578623538764912642195378719382456
123456789759283614486971253342768591891542367567319428935127846278694135614835972
123456789849173256765298431586941372291735648437862915352617894978524163614389527
123456789784913652569827134316598247845271963297634815652149378938765421471382596
123456789496817235587329461864275193359184627712693854631942578978561342245738916
123456789746198532859732146298314675374569821615287394967845213481623957532971468
123456789867239145954781362392567418416928573578143926745692831281375694639814257
123456789475981362869327541654813927791642853382795614938164275516279438247538196
123456789968137524457892136892374651716285493534619872685943217279561348341728965
123456789645987312897312645972863451536124897418579236364291578289735164751648923