Killer Sudoku Online (Logical Thinking Brain Game)

In this game there will be a grid of 9 x 9 blocks, this grid is further divided into 9 subgroups of 3 x 3 blocks, in addition to that, the blocks will be grouped by red clue lines marked with a number. The object of this game is to fill in all the blocks with 1 - 9 without repeat within either the rows or columns or the subgroups or the clue groups. Moreover, the numbers in a clue group must add up to the number given in the clue. This game is similar to Sudoku but more challenging.
Killer Sudoku is also known as with other names e.g Addoku, Sum Sudoku and in Japan Samunamupure.