PUZZLE #4190: Four Color Theorem (diff 3)

four-color learn difficulty: 3/7 reasoning author: system unsolved

Planar graph: A: B,C,D; B: A,C,D; C: A,B,D; D: A,B,C. Color each region with colors 1-4 so adjacent regions differ.

DATA

Adjacency	{ "A": [ "B", "C", "D" ], "B": [ "A", "C", "D" ], "C": [ "A", "B", "D" ], "D": [ "A", "B", "C" ] }
Nodes	`A, B, C, D`
Target	`C`
Hint	`Assign colors greedily: for each node, pick the smallest color not used by its neighbors. What color is node C?`
Answer Format	`color label (e.g., 'c2') for the target node`

{
  "type": "four-color",
  "adjacency": {
    "A": [
      "B",
      "C",
      "D"
    ],
    "B": [
      "A",
      "C",
      "D"
    ],
    "C": [
      "A",
      "B",
      "D"
    ],
    "D": [
      "A",
      "B",
      "C"
    ]
  },
  "nodes": [
    "A",
    "B",
    "C",
    "D"
  ],
  "target": "C",
  "hint": "Assign colors greedily: for each node, pick the smallest color not used by its neighbors. What color is node C?",
  "answer_format": "color label (e.g., 'c2') for the target node"
}

author's note: Pool fill: four-color diff 3