Backtracking is a recursive algorithm strategy where we backtrack when a result is not found and continue search for solution in other possible ways. Backtracking is a popular way to solve many famous problems, especially chess, Sudoku, crosswords, and so on. Since recursion is the key component of backtracking, we need to ensure that our problem can be divided into sub problems, and we apply recursion into those sub problems. In this section, we will solve one of the most popular games, Sudoku, using backtracking.
In Sudoku, we have a partially filled box with nice boxes of size 3X3. The rule of the game is to place a number 1 to 9 in each cell, where the same number cannot exist in the same row or column. So, in the 9X9 cell, each number 1 to 9 will be present only once for each row and each column:
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7 |
3 |
8 |
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2 |
5 |