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UVA - 12041 BFS (Binary Fibonacci String)
Description
Problem B - BFS (Binary Fibonacci String)
We are familiar with the Fibonacci sequence (1, 1, 2, 3, 5, 8, ...). What if we define a similar sequence for strings? Sounds interesting? Let‘s see.
We define the follwing sequence:
BFS(0) = 0
BFS(1) = 1 (here "0" and "1" are strings, not simply the numerical digit, 0 or 1)
for all (n > 1)
BFS(n) = BFS(n - 2) + BFS(n - 1) (here, + denotes the string concatenation operation). (i.e. the n-th string in this sequence is a concatenation of a previous two strings).
So, the first few strings of this sequence are: 0, 1, 01, 101, 01101, and so on.
Your task is to find the N-th string of the sequence and print all of its characters from the i-th to j-th position, inclusive. (All of N, i, j are 0-based indices)
Input
The first line of the input file contains an integer T (T ≤ 100) which denotes the total number of test cases. The description of each test case is given below:
Three integers N, i, j (0 ≤ N, i, j ≤ 231 - 1) and (i ≤ j and j - i ≤ 10000). You can assume that, both i and j will be valid indices (i.e.0 ≤ i, j < length of BFS(N)) .
Output
For each test case, print the substring from the i-th to the j-th position of BFS(N) in a single line.
Sample Input
3
3 1 2
1 0 0
9 5 12
Sample Output
01
1
10101101
题意:0,1, 01, 101, 01101.....每个串都是前两个串的连接,输出第n个串的第i到j位
思路:因为第n个串是第n-2个串+第n-1个串,所以我们所以我们像对树的搜索一样,递归下去
#include <iostream> #include <cstring> #include <cstdio> #include <algorithm> typedef long long ll; using namespace std; const int maxn = 111; ll f[maxn]; int n, x, y; void init() { f[0] = f[1] = 1; for (int i = 2; i < maxn; i++) f[i] = f[i-1] + f[i-2]; } void bfs(ll l, ll r, int cur, int sign) { if (y < l || x > r) return; if (l == r) { printf("%d", sign); return; } bfs(l, l+f[cur-2]-1, cur-2, sign); bfs(l+f[cur-2], r, cur-1, 1-sign); } int main() { init(); int t; scanf("%d", &t); while (t--) { scanf("%d%d%d", &n, &x, &y); int cnt; for (int i = 0; i <= 50; i++) if ((i % 2 == n % 2) && f[i] > y) { cnt = i; break; } int sign = cnt % 2; bfs(0, f[cnt]-1, cnt, sign); printf("\n"); } return 0; }