Sudoku puzzles are a relatively recent creation. Their popularity is partly due to the very simple and easily understood rules of the puzzle. Using a few entry-level strategies, even a beginner can enjoy solving a wide range of Sudoku puzzles.
An American, Howard Garns, created the first Sudoku puzzles in 1979. Their popularity increased over the next few years, and a Japanese publisher gave the puzzles the name, "Sudoku," in 1986. The name is an abbreviation of a Japanese phrase that roughly means, "The digits may occur only once."
Indeed, that is the essence of the rules of Sudoku puzzles. The standard puzzle is a square grid of 9 squares by 9 squares with 3x3 blocks marked off inside the larger grid. The objective of the puzzle is to fill the boxes with the numerals 1 through 9 so that no row or column or 3x3 block uses a numeral more than once. It is a puzzle of simple number placement as no mathematics is applied to the numbers.
Scanning is the simplest strategy to use to solve part or all of the puzzle. Puzzles that are labeled "easy" can generally be solved using just the scanning strategy. A scan of a new puzzle should be the first step, and scans are performed periodically thereafter. For the sake of consistency, the numbers 1-9 should be scanned in order.
The scanning process consists of checking across each row of a group of 3 rows to see if the target number occurs. If the target number occurs in two rows, then by process of elimination the puzzle solver can conclude that the number must occur in the remaining row of the 3x3 block that does not contain that number. A vertical scan then will often eliminate that number from the vertical columns of the target group. The remaining square is the square where the target number belongs.
Marking up is the second simple strategy that can be used to help solve the Sudoku puzzle. Occasionally, the scan process will reduce the possible squares where a target number belongs to two or three squares. When that happens the puzzle solver can "mark up" the square with the possible solutions, and then use another strategy to reduce the possibilities to only one, the correct solution. The mark up process usually consists of penciling in the possible solutions with small numerals that can later be erased.
Analysis is a third strategy that is typically used to solve the puzzle. After several scans and the marking up process it is often possible to eliminate candidates from cells, leaving only one choice. For example, finding a matched group can help with this kind of analysis. If two squares within a row or column or 3x3 block contain the same two candidates, then they are "matched." Placing that candidate in any other row or column or 3x3 would lead to an impossible solution, which means that if that candidate is marked up in any other row or column it can be erased.
Another analytical approach is to postulate a "what if" question. When a candidate numeral has been limited to one of two choices, then a guess is made. The question is asked, "What if I put the numeral here, what will happen?" The logical thread is followed with placement of numerals into other squares, and if a logical contradiction is reached, such as a numeral appearing twice or not at all, then the conclusion is that the other numeral should have been selected in the original guess. Of course, this approach requires more thought, memory, and pencil work than the other strategies.
Sudoku puzzles have attained great popularity in a short period of time because they are challenging but solvable, and above all, great fun. Mastering these few strategies will help the beginner enjoy the challenge and the fun.