  This paper is concerned with the popular Sudoku problem. We proposed a warm
restart strategy for solving Sudoku puzzles, based on the sparse optimization
technique. Furthermore, we defined a new difficulty level for Sudoku puzzles.
The efficiency of the proposed method is tested using a dataset of Sudoku
puzzles, and the numerical results show that the accurate recovery rate can be
enhanced from 84%+ to 99%+ using the L1 sparse optimization method.
