Simple Coloring (or Single's Chain) is an easy-to-understand strategy because it uses no complex math—just two colors, like Blue and Green.
It works by tracking a single number (e.g., "Where can the 2s go?").
Interactive Example
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Click "Apply Logic" to see the strategy in action.
Real Example Explanation
In the example above, we are tracking the number 2.
- The Chain:
- We look for "Strong Links" (rows, columns, or boxes where 2 appears exactly twice).
- We pick a starting pair and color one Blue and the other Green.
- If a Blue cell is connected to another pair, the other end becomes Green (and vice versa).
- This creates a "Daisy Chain" of alternating colors across the grid.
- The Logic:
- Since every link is an "either/or" choice, the entire Blue set is tied together, and the entire Green set is tied together.
- Scenario A: All Blue cells are 2 (and Greens are not).
- Scenario B: All Green cells are 2 (and Blues are not).
- Result: The real 2s are either all the Blues or all the Greens.
- The Elimination (Type 2):
- Look at cell R3C2.
- It sees a Blue candidate (at R3C9).
- It also sees a Green candidate (at R6C2).
- Since one of those colors must be real, it is impossible for R3C2 to be a 2. (If it were 2, it would break both the Blue chain and the Green chain).
- Therefore, we remove 2 from R3C2.
How to Spot It
- Pick a Number: Focus on one candidate (like 2).
- Find Pairs: Look for houses (row/col/box) where that number appears exactly twice.
- Start Coloring: Mental or pencil. Mark the first one A (Blue) and the second B (Green).
- Extend: If a Blue cell connects to another pair, mark the new partner Green.
- Check for Conflict:
- Type 1 (Chain Broken): If two cells of the same color see each other, that color is false. (All cells of that color are removed).
- Type 2 (Intersection): If an uncolored cell sees both colors, remove the candidate from that cell.
Comparison
- Remote Pairs: Uses a chain of pairs (two numbers).
- Simple Coloring: Uses a chain of single numbers.
- X-Wing: A very short Simple Coloring chain (length 4).