276. Paint Fence

Posted 2020-08-09 Machelsky

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.

思路：最多两个相邻同色。之前不同色＊（k-1)＋之前同色＊(k-1)就是现在不同色的个数。最后输出现在不同色加现在同色的总个数。

public class Solution {
    public int numWays(int n, int k) {
        if(n<=0||k<=0)
        {
            return 0;
        }
        if(n==1)
        {
            return k;
        }
        int same=k;
        int diff=k*(k-1);
        for(int i=2;i<n;i++)
        {
            int pre=diff;
            diff=(diff+same)*(k-1);
            same=pre;
        }
        return diff+same;
    }
}