10918 - Tri Tiling（数论 规律）

Problem D: Tri Tiling

In how many ways can you tile a 3xn rectangle with 2x1 dominoes?

Here is a sample tiling of a 3x12 rectangle.

Input consists of several test cases followed by a line containing -1. Each test case is a line containing an integer 0 ≤ n ≤ 30. For each test case, output one integer number giving the number of possible tilings.

Sample input

2812-1

Output for Sample Input

31532131

题意：给定n求出n*3又1*2拼成需要几种。

思路：自己推的公式错了。。哎。。没考虑清楚，后来看题解http://www.cnblogs.com/staginner/archive/2011/12/16/2290020.html

代码：

#include <stdio.h>#include <string.h>int n;int f[35];void init() {f[0] = 1; f[2] = 3;for (int i = 4; i <= 30; i ++) {f[i] = 4 * f[i - 2] - f[i - 4];}}int main() {init();while (~scanf("%d", &n) && n != -1) {printf("%d\n", f[n]);}return 0;}