杀手数独中的45法则是什么？
最后更新
45规则是杀手数独中最强大的单一技巧。掌握它，你几乎可以在每个谜题中解锁自由数字，无论难度如何。
为什么每个单元之和为45
每行、每列和每个3×3宫必须恰好包含数字1到9一次。由于1+2+3+4+5+6+7+8+9 = 45，每个完整单元的总和恰好为45。这是一个固定的数学事实——在任何有效的数独解中都不可能不同。
如何应用规则
步骤1：选择一个单元（行、列或宫）。
步骤2：将所有完全位于该单元内的笼的和相加。
步骤3：注意任何其笼跨越单元边界的单元格。
步骤4：45减去步骤2的总和得到那些跨越单元格的和。
如果只有一个单元格跨越边界，其确切值就是45减去笼和的总和。你得到一个自由数字。
示例解析
Suppose box 1 (top-left 3×3) has cages summing to 38 entirely within it. One additional cell from a cage extends outside box 1. That cell must equal 45 - 38 = 7. Place 7 immediately.
Now suppose the total of entirely-contained cages is 31, and two cells from external cages cross into the box. Those two cells together sum to 45 - 31 = 14. Their candidates are restricted to pairs summing to 14: {5,9}, {6,8}.
跨多个单位扩展
The 45 rule can be applied to combinations of units. Two rows together must sum to 90. Three boxes in a band must sum to 135. This extended form can resolve multi-cell innies and outies that span several units, giving you sum constraints even when no single cell is fully determined.
内化这个最快的方法是在棋盘上—— 在线玩杀手数独 并在实时谜题上应用它。