Function to reverse an array . An array can be reversed in O ( n ) time and O ( 1 ) space .
def reverse ( arr , l , r ) : NEW_LINE INDENT if l < r : NEW_LINE INDENT arr [ l ] , arr [ r ] = arr [ r ] , arr [ l ] NEW_LINE l , r = l + 1 , r - 1 NEW_LINE reverse ( arr , l , r ) NEW_LINE DEDENT DEDENT