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Last Remaining Cell in Sudoku
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Last Remaining Cell

The Very First Technique Every Solver Learns

By Minimal Sudoku TeamLast updated:

The Last Remaining Cell is the simplest Sudoku technique — so simple it barely counts as a strategy. When a row, column, or box has only one empty cell, you can immediately fill it with the only missing digit.

Quick Summary
  • What: A row, column, or box with only one empty cell
  • How: Find which digit (1-9) is missing, place it
  • Difficulty: Absolute beginner — no thinking required
  • When: Usually appears in the late game when the grid is nearly full

The Concept

Every row, column, and 3×3 box must contain each digit 1-9 exactly once. If a unit has 8 digits placed and only 1 empty cell, simple subtraction tells you what goes there.

This technique requires no candidate analysis or complex logic — just count what's missing.

The Golden Rule

📍 Last Remaining Cell Rule
When a row, column, or box has exactly one empty cell, that cell must contain the only digit (1-9) not yet present in that unit.

How to Find Last Remaining Cells

1

Scan for nearly-complete units

Look for rows, columns, or boxes with 8 filled cells.
2

Find the empty cell

There's only one — you can't miss it.
3

Identify the missing digit

Count 1-9 and find which one isn't present: 1, 2, 3... got them all except 7? It's 7.
4

Fill it in

Place the digit and look for chain reactions!

Example

Last Remaining Cell in a Box

Box with one empty cell

The center box (Box 5) has 8 cells filled:

  • Present: 1, 2, 3, 4, 5, 6, 8, 9
  • Missing: 7
  • Empty cell: R5C5
Solution
R5C5 = 7. No other analysis needed!

Chain Reactions

Last Remaining Cells often trigger chain reactions. When you fill one:

Endgame Cascade
In the final stages of a puzzle, filling one Last Remaining Cell often creates another, then another. You can solve the last 5-10 cells in seconds this way.

Tips

Quick Mental Math
Add up the present digits: 1+2+3+4+5+6+7+8+9 = 45. If your unit totals 38, the missing digit is 45-38 = 7. Faster than checking each digit!
Rare in Early Game
You won't find many Last Remaining Cells at the start of a puzzle. This technique shines in the endgame when units are nearly complete.
Check All Three Unit Types
A cell belongs to a row, a column, AND a box. Check all three — you might spot a Last Remaining Cell in any of them.

Related Techniques

Once you've mastered this, learn these slightly more complex beginner techniques:

Next Steps

1️⃣Naked Single🔎Hidden Single👀Scanning Technique
Naked SingleBeginner

Naked Single

When a cell has only one possible candidate — the next step up from Last Remaining Cell.