add the difficulty level
Merge branch 'mathFrankxin'
add share title
Merge branch 'mathFrankxin'
fix bugs
fix some buggs
fix some buggs
Merge branch 'mathFrankxin'
fix some bugs
fix some bugs
fix some bugs
fix some bugs
fix bugs
Merge branch 'mathFrankxin'
fix some bugs
fix some bugs
fix some bugs