[Swift]LeetCode276. 粉刷栅栏 $ 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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有一个有N根柱子的栅栏，每根柱子都可以涂上一种K颜色。 

你必须把所有的柱子都刷上油漆，这样两个相邻的栅栏柱子就不会有相同的颜色。 

返回可以绘制围栏的方法总数。 

注：

n和k是非负整数。

---

Solution:

class Solution {
    func numWays(_ n:Int,_ k:Int) -> Int {
        if n == 0 {return 0}
        var same:Int = 0
        var diff:Int = k
        for i in 2...n
        {
            var t:Int = diff
            diff = (same + diff) * (k - 1)
            same = t
        }
        return same + diff
    }
}