填入1~4（黑格不填数），使得每行、列、宫内数字不重复。
Fill in the squares (without black squares) with digits from 1 to 4 so that no digit is repeated in a row, column or outlined box.
标准数独基础上，题目左侧的两个提示数字在该行中左右对称。
Classic rules applied. Additionally, two digits at the left side are bilateral symmetry on the row (without sequence).
标准数独基础上，提示是其周围数字的和。
Classic rules applied. Additionally, numbers in circle is the sum of the numbers around it.
标准数独基础上，提示是其周围数字行列式运算后的结果。
Classic rules applied, the clue is the result of the determination.
标准数独基础上，每条线上数字是多位数质数（左→右，上→下）。
Classic rules applied. Additionally, numbers are multi-digit prime (left-right, up-down) on each line.
标准数独基础上，每条线上的数字按顺序从一端到另一端是一组等差数列。
Classic rules applied. Additionally, on each line, numbers form arithmetic sequence in order from one side to another side.
标准数独基础上，相同字母表示相同数字，不同字母表示不同数字。
Classic rules applied. Additionally, same letter means same number, different letters mean different numbers.
标准数独基础上，涂色格子填入奇数。
Classic rules applied. Additionally, colored cells contain odd numbers.
标准数独基础上，提示表示其相邻两格乘积的十位上的数值。
Classic rules applied. Additionally, if a digit is marked between two cells, then it's same to the tens place of the product of the two digits in the grids.
填入1~N，使得紧邻任一直线，且在同一侧的一组单元格内数字不同。
Write 1~N, to each line, the groups of cells adjacent to line and be on one side cannot own repeated numbers.
