URAL 1225. Flags (DP)

1225. Flags
Time limit:1.0 Second
Memory limit:64 MB
On the day of the Flag of Russia a shop-owner decided to decorate the show-window of the He shop with textile stripes of whit E, blue and red colors. He wants to satisfy the following conditions:

1. Stripes of the same color cannot is placed next to all other.
2. A blue stripe must always being placed between a white and a red or between a red and a white one.

Determine the number of the ways to fulfill his wish. Example.For N= 3 result is Following:input N, the number of the stripes, 1≤ N≤45.output M, the number of the ways to decorate the shop-window. Sample

input	Output
3	4

Test instructions: Coloring problem. Adjacent colors can not be the same, blue can only appear between red white or white red.

Parsing: recursion.

Consider the color of the position I: if red or white, you only need to add a white or red in the back of the i-1, if the blue, then the i-1 will be red or white, you only need to add red or white in the back of the i-2.

Must be a long long, otherwise WA on Test 12.

AC Code:

#include <cstdio>long long F[50];int main () {    f[1] = f[2] = 2;    for (int i=3; i<=50; i++) f[i] = F[i-1] + f[i-2];    int n;    while (scanf ("%d", &n) ==1) {        printf ("%lld\n", F[n]);    }    return 0;}

URAL 1225. Flags (DP)