双层巴士 Bus

双层巴士是算式数独的一种。在2014年，世界数独锦标赛即将于英国举办，爱好者们举办了一场以英国风格为主题的热身赛，著名的网球和双层巴士都被设计成了题目。

Bus is a type of Calculation. In 2014, World Sudoku Championship would be held in the UK, sudoku fans held a warm-up competition with British theme, tennis and double-decker bus are designed as Tennis and Bus.

标准数独基础上，每个涂色区域中上方的三个数字乘积，等于下方的三位数。因此这个题型本质上是带着固定形状的算式数独。

Classic rules applied, three numbers above product to the 3-digit number below in each colored zones. So it is just the Calculation with certain shape.

基础方法和算式类似，奇偶性和因数5一般都是入手点。此外一些数字太小了以至于不能作为因数，例如1，以及一些情况下的2或3。乘积的百位也只能是1~4，因为7x8x9=504，但是0不能出现在结果之中。

Basic ways are like Calculation, parity and factor 5 are always the keys. And also, some numbers are too small to be factors such like 1, and 2 or 3 in some situations. The hundreds of the product can only be 1~4, for 7x8x9=504, but 0 cannot appear.