How to Solve Easy as ABC Puzzles
Easy as ABC, also known as ABC End View, or Last Man Standing, is another puzzle with a murky history. It seems to be a popular staple in variety puzzle magazines, but I was unable to find any information about its origin or evolution. It falls generally into the Latin Square family, because you’re not allowed to repeat a letter in any row or column. What makes it interesting is that you also have to account for one or more empty cells in each row and column.
Rules
Given a range of letters (usually A through C), place them into the grid so that they each appear one time in every row and column. Commonly, the grid is also larger than required, so empty cells are part of the solution.
- Place each letter in the range exactly one time in every row and column.
- Any extra cells remain empty.
- Letters outside the grid show which letter is first seen from that position.
Basic Techniques to Solve
- Start with the letter that has the most clues.
- For each letter, find cells where it can’t exist.
- Watch clue intersections..
Start with the Most
Similar to cryptography, the best way to begin solving is by looking for something common. For code-breakers, that would be common word patterns, or frequent occurrences of the same letter. In the case of this puzzle, starting with the most common clue allows you to narrow down the options for other clues later. Simply count each letter outside the grid, and start the process of the following tips with the letter that shows up the most times.
In our example, A and B both have 5 clues, while C only has 3.
Narrowing it Down
Now that you’ve focused on a single letter, examine the rows and columns that it views. First, count how many possible letters there are versus the size of the grid. All letters must appear, so that tells you the letter you’re focused on can’t be too close to the other end of its row or column. For example, if you’re looking for A through D in a 5×5 grid, and you’re focused in a row where C is the first letter, it must show up at least 4 cells away from the far end of the row. Otherwise, there wouldn’t be room for the other 3 letters required. So you can eliminate 3 cells for the C.
Let’s look at the As. Since we need 3 letters, they can’t appear in the last 2 cells of their row or column. 
If we do the same for the B’s, these are the cells they can’t appear in. 
Finally, this is what we see when we look only at the Cs. As you can see, this alone isn’t enough information.
Pencil marks help here. Marking possible candidate positions reveals more eliminations you can make, simply because a letter can’t appear earlier than the clue given for that row or column.
Be careful while marking candidates! Never assume that reducing the letters to one possibility in a cell means you’ve solved it.. Remember that most Easy as ABC puzzles contain empty cells, so pencilmarks might get you down to the same single letter in multiple positions. However, if you see that a letter can only exist in one cell out of the whole row or column, then that must be correct.
This is the same information from before. But instead of blocks where a letter can’t appear, we show the remaining places each letter may appear. 
Next, we make another pass around the grid, eliminating those letters which cannot appear before the clue letter. 
Notice now we have two columns where a letter appears only once. Column 1, Row 3 must be an A, and Column 6, Row 2 must hold a B.
Watch the Intersections
While you’re examining each letter, pay attention to the clues that cross the current row and column. Sometimes, you’ll simply see that a different letter must occur in a certain cell. However, the most useful thing you can spot is cells which can’t hold any letter. Once you know a cell must be empty, shade it completely, and that will help guide your focus for the other letters.
In Column 4, we see the B must be in Row 3. The clue crossing from the right means the C must be in Column 6. Now we know the rest of the row must be blank.
Solving the Puzzle
Now that we have the basics down, let’s apply the concepts to the rest of the example puzzle.
Initial Deductions
This is the current state of the puzzle after the tips above. 
Here, the A must appear above the other letters in Column 6. 
The blocked cell in Column 5 means the B can’t be in Column 4, because the C must appear after the B.
We can apply the same eliminations for these C, B, and A clues. 
On the other hand, here we eliminate letters which can’t appear before their clues. 
And now, in Column 5, we’re left wwith a single A, so it must appear in the bottom row.
Gaining Ground
In these two rows, the B can’t appear in the Column 4, because they must leave room for the other 2 letters. 
Notice the B only appears in Columns 1 and 2 in these two rows. Therefore, B can be eliminated in other rows.. 
Now, we can solve these cells, where they hold the only remaining B in their row or column.
We’re down to only one position for C in Column 3 and Row 6.So we can solve these two cells. 
This reveals three more cells with the final position for a letterin their row or column . 
This of course, reveals the final C in the grid, in Column 4, Row 1.
Wrapping Up
Now at this point, it looks like we might have to guess to figure out the positions of the final As and Bs. 
But wait! In this row, the B is supposed to be the first visible letter. So the A can’t be in Column 2. 
Once we’ve eliminated that A, we can easily see the correct positions of the final two instances.
Naturally, we can now see the position of the final two Bs, as well. 
We’ve solved the Easy as ABC puzzle!
