摩天楼 Skyscrapers
摩天楼是一种变型数独，但是规则难以理解，尤其是对某些初学者。
Skyscrapers is a kind of variant sudoku, with a rule difficult to understand, especially for some newcomers.
◆为了理解规则，你可以把盘面视为一个楼盘，数字是里面的大楼。数字X意味着楼的高度是X。
To understand the rules, you can regard the grid as a plant, and the numbers are skyscrapers. Number X means the skyscrapers' height is X.
在上面的案例里，我们从左边看，能看见2和3，1被2挡住了。这时我们能看见两栋楼，因此外侧的提示是2。
In this example, we see from left, we can see the skyscraper 2 and 3, 1 will be hidden by 2. Now, 2 skyscrapers can be seen, the outside clue is 2.
从右边看只能看见3，因为1和2都会被挡住，因此外侧的提示是1。
When you see from the right, you can only see the skyscraper 3, because 1 and 2 are all hidden. Now, only 1 skyscrapers can be seen, the outside clue is 1.
你也可以通过这张图去理解规则。
You can also use this pic to understand the rules.
This pic comes from @SunnieShine
◆最大的数字N The largest number N
最大的N在最外侧的时候，它外面的提示必定是1，反之亦然。
If the largest number N is in the outermost side, the outside clue must be 1, vice versa.
◆第二大的数字N-1 The second number N-1
① 最外侧的每边都必须有N-1的数字，对应的外提示必定是2。
There must be a clue 2 in each side with the outside number as N-1.
② 外提示是2时，N-1不能在第二格。
N-1 cannot be in the second cell when the outside clue is 2.
③ 如果N在末端，而提示是2，首位必定是N-1。
If N is at the end of Row/Column, and the clue is 2, the first number must be N-1.
④ 如果N在倒数第二格，第一格只能是N-1或N-2。
If N is at the second cell of the end, the first number can only be N-1 or N-2.
⑤ 如果两侧的提示都是2，必定有一侧第一格是N-1。
If both of the sides' clue are 2, one of the end must be N-1.
◆数字1 Number 1
如果所有数字都能被看见，1必定是第一个。
If all the numbers can be seen, 1 must be as the first number on one side.
◆过大的提示 Too-large clues
① 提示M，对于任意i≤M，第i格的取值范围是[1, i+(N-M)]。
If the clue is M, to ∀i≤M, the ith cell should have the range of [1, i+(N-M)].
② 提示M，N在第M格，对于任意i≤M，第i格的取值范围是[i, i+(N-M)]。
If the clue is M, and N is in the Mth cell, to ∀i＜M, the ith cell should have the range of [i, i+(N-M)].
◆两侧提示之和 Sum of both sides clues
① 两侧提示和是N+1时，所有楼都会被看见。
If the sum of the both side clues is N+1, then all the numbers will be seen.
② 提示和较大时，你可以尝试摆放较大数字的位置。
You can try to put the large number when the sum of both side is large.
◆一组拐弯数字 A group of 1~N turning
◆提示定顺序 Order by clue
◆缺一格结构 K numbers with K-1 clue
◆整体上而言，与其他标准或变型进行比较，观察行列在摩天楼里更为重要。
Generally, compared to other variant or Classic, views about Rows and Columns are more important in this type.
练习 Practice
① 在六阶摩天楼数独中，B1旁边的提示是5，B1最大是______。
In 6x6 Skyscrapers, clues adjacent to B1 is 5, B1 can at most be ______.
② 在六阶摩天楼数独中，一行两侧有两个提示，它们的和最大是______。
In 6x6 Skyscrapers, there are 2 clues on both sides of one Row, their sum can at most be ______.
③ 解答问号格 Find out the ？cell.
答案 Answer
① 2 ② 7 ③ E1=4
