10918 - Tri Tiling(数论 规律)

Problem D: Tri Tiling

In how many ways can you tile a 3x n  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

2
8
12
-1

Output for Sample Input

3
153
2131

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;
}


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