Irregular Killer Sudoku 4x4

Irregular Killer Sudoku 4x4 Rules：

• Each row, column, and 2x2 block must contain each of the digits 1 to 4 exactly once.

• The sum of the digits in each region must match the number in its corner.

• No digit can appear more than once in a region.
  - Irregular Sudoku Rule: Each row, column, and irregularly shaped block must contain all the digits (1-4) without repetition. This is the key difference.

The 45 rule is a fundamental solving technique in Killer Sudoku that utilizes the fact that the sum of the digits in each row, column, and 3x3 block in a completed Sudoku puzzle always equals 45. This rule stems from the principle that each digit from 1 to 9 must appear exactly once in each row, column, and 3x3 block.

Irregular Killer Sudoku 4x4 puzzle：

Irregular Killer Sudoku 4x4 solution：