![]() ![]() IsAllowed() method uses above three methods to check if it is safe to assign number in the cell. Private boolean containsInBox(int row, int col,int number) Private boolean containsInCol(int col,int number) Private boolean containsInRow(int row,int number) private boolean containsInRow(int row,int number)īelow three methods are used to check, if number is present in current row, current column and current 3X3 subgrid or not. 0 value in any of its cell, is considered to be incomplete or wrong. Instance variable sudoku can be initialized using any of the below two constructors.Īll the cells of completely solved sudoku array must have assigned valid values. Sudoku, 9×9 int array is used to store all the elements of sudoku. Backtracking is also known as depth-first search.Īpproach for solving sudoku using recursive backtracking algorithm ![]() But backtrack to where? to the previous choice point. Think of a labyrinth or maze – how do you find a way from an entrance to an exit? Once you reach a dead end, you must backtrack. ![]() Briefly, once you exhaust all your options at a certain step you go back. If at some step it becomes clear that the current path that you are on cannot lead to a solution you go back to the previous step (backtrack) and choose a different path. In backtracking algorithms you try to build a solution one step at a time. Sudoku can be solved using recursive backtracking algorithm. For other Backtracking algorithms, check my posts under section Backtracking (Recursion). If you are interested in java programs for other board games like Sudoku Checker, Tic Tac Toe, Snake N Lader and N Queen Problem , you can check out my posts in Board Games section. If you are looking for program to check correctness of Sudoku, you will find it in my post Sudoku checker (By traversing each cell only once). This post is about generating solution for sudoku problem and not for checking if solution is correct or not. ![]()
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