One of the most enduring and consistently hard challenges is posed by Alphabet Echo.
The task is, on the face of it, a fairly simple one. Place the 26 letters of the alphabet, twice, into a 7x8 square grid, leaving four squares empty. Make sure that no horizontal, vertical or diagonal line contains the same letter twice, nor a pair of consecutive letters. There are plenty of extra pieces of information to help, such as a comprehensive list of letters which are repeated in consecutive rows or columns or in any half of the grid (the central column of the seven is considered to be in both 'halves'). For every row and column, the solver is informed how many vowels and how many letters from the first half of the alphabet are used. There are typically a few other nuggets added as well, such as a three letter fragment which can be read in a particular direction somewhere in the grid, or some information about how the blank squares are placed.
But all of this information is carefully crafted to be only barely enough to provide a unique solution, and it can prove awkward to assimilate it all – often only one element of the information provides the next step of the puzzle. The challenge is to work out which piece of information is the next important one!
As well as the sample puzzle, a handy checksheet is provided here (download the extra details file) to show at a glance which letters belong in which part of the grid and make it immediately apparent when letters are ruled in or out of appearing in a particular row or column.
In the grid, each letter of the alphabet appears twice and there are four blanks. Neither the same nor any two consecutive leters of the alphabet appear in the same row, column or diagonal. A and Z are not treated as consecutive in this puzzle. Beside each row and column appear two numbers; the black number shows how many vowels appear in that row or column and the blue number shows how many letters are in the first half of the alphabet, ie A-M. Using the additional clues provided, can you complete the grid.