514. Paint Fence

class Solution {public:    /*     * @param n: non-negative integer, n posts     * @param k: non-negative integer, k colors     * @return: an integer, the total number of ways     */    int numWays(int n, int k) {        // write your code here        if (n==0)            return 0;        if (n==1)            return k;        if (n==2)            return k*k;        int x=k*(k-1),y=k;        for (int i=3;i<=n;i++){            int tmp=x;            x=(x+y)*(k-1);            y=tmp;        }        return x+y;    }};