Fourth level hard Sudoku puzzle 6, Strategies Techniques and Solution
This is the 6th puzzle session at fourth level of hardness of very hard category. This is a very hard puzzle with multiple bottlenecks to overcome right from the start. Valid DS evaluation for empty cells needs to be done early but in selected cells and limited to 3 digit long DSs. Cross-scan of row, column and 9 cell square, Digit subset analysis, Single digit lockdown and advanced use of Cycles provide the main breakthroughs. Solution of each step with strategies and techniques adopted are explained fully ...