Double Sudoku (646)

Instruction:

Place a digit from 1-4 in each empty cell so that each digit appears exactly twice in each row, column, and outlined region. Identical digits cannot share an edge.

Reference: WPF (1)

Examples:

WPF Sudoku GP 2014 - Playoffs (119)

WPF Sudoku GP 2014 - Round 4 (115)

Parent puzzle:
Sudoku