Killer Sudoku

Killer Sudoku is a well-known twist on Sudoku. It adds more stuff instead of starter numbers. The rules are as follows: Place the digits from 1-9 into each row, column and 3x3 box once. The numbers in an inner shape (marked by dots) must add up to the number at the top-left corner of that inner shape. No number can be repeated in an inner shape. Killer Sudoku is in newspapers like The Guardian!