[Swift]LeetCode276. 粉刷柵欄 $ Paint Fence

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There is a fence with n posts, each post can be painted with one of the k colors.

You have to paint all the posts such that no more than two adjacent fence posts have the same color.

Return the total number of ways you can paint the fence.

Note:

n and k are non-negative integers.

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有一個有N根柱子的柵欄，每根柱子均可以塗上一種K顏色。 

你必須把全部的柱子都刷上油漆，這樣兩個相鄰的柵欄柱子就不會有相同的顏色。 

返回能夠繪製圍欄的方法總數。 

注：

n和k是非負整數。

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Solution:

 1 class Solution {
 2     func numWays(_ n:Int,_ k:Int) -> Int {
 3         if n == 0 {return 0}
 4         var same:Int = 0
 5         var diff:Int = k
 6         for i in 2...n
 7         {
 8             var t:Int = diff
 9             diff = (same + diff) * (k - 1)
10             same = t
11         }
12         return same + diff
13     }
14 }