ABC End View

ABC End View (also known as Easy as ABC, Buchstaben, or Skyscraper Letters) is a logic puzzle where the player fills an NxN grid with letters and empty cells. The grid uses the first few letters of the alphabet (e.g., A, B, C for a 5x5 grid), with some cells left blank. Clues around the border indicate which letter is seen first when looking into the grid from that direction. The solver must deduce the placement of all letters using these visibility clues and the constraint that each letter appears exactly once per row and column.

Rules

1. Fill the NxN grid so that each row and each column contains each letter exactly once (e.g., A, B, C in a 5x5 grid). The remaining cells in each row/column are left empty.
2. Clues on the edges of the grid indicate the first letter visible from that direction when looking across the row or down the column (skipping empty cells).
3. Not all edges have clues — missing clues provide no information.
4. Typically, for an NxN grid, use N-2 different letters (leaving 2 empty cells per row/column), though this can vary.

Strategies

• Direct Placement: If a clue shows "A" at the edge, the letter A must be in the first non-empty cell from that direction. In some cases, this forces A to be in the very first cell.
• Last Letter Clue: If the clue is the last letter alphabetically used in the puzzle (e.g., "C" in an A-B-C puzzle), it can appear anywhere in the row as long as no other letter precedes it from that direction. This often means it's in the first cell.
• Opposite Clues: When two opposite edges of the same row/column both have clues, the combined constraints can significantly narrow down letter positions.
• Cross-referencing: A letter's position must satisfy both its row clues and its column clues simultaneously. Check intersections.
• Empty Cell Deduction: If you know where the letters go, the remaining cells must be empty, which can inform clues in the perpendicular direction.
• Unique Candidate: If a letter can only go in one cell within a row or column (after elimination), it must go there.

ABC End View emerged from the tradition of Latin square puzzles, which have been studied mathematically since the 18th century through Leonhard Euler's work. The specific format of adding visibility clues from the border was developed in the puzzle community during the 1990s and early 2000s.

The puzzle is closely related to Skyscrapers (which uses the same visibility mechanic with numbers and building heights). The key difference is that ABC End View uses letters and includes empty cells, which adds an extra layer of deduction. The puzzle appears under various names in different countries: "Easy as ABC" in English-speaking regions, "Buchstaben" (Letters) in German puzzle magazines, and other names elsewhere.

ABC End View has been a regular feature in the World Puzzle Championship since the early 2000s, where it is valued for its clean logic and elegant difficulty scaling. The puzzle can be made easier or harder by adjusting the grid size, the number of letters used, and the number of border clues provided.

The puzzle is particularly popular in German and Eastern European puzzle communities, where puzzle magazines have published it extensively. It has also found a home in educational settings, where it is used to teach logical reasoning without requiring mathematical knowledge. The letter-based format makes it accessible to younger solvers and those who might find number-based puzzles intimidating. Today, ABC End View remains a respected classic in the logic puzzle world, appearing in competitions, books, and digital puzzle platforms.