注意到当$a_{i}\ne 1$且$a_{i+1}\ne 1$,那么$\forall i<j,a_{j}=a_{i+1}$(证明的话简单归纳就可以了) 令$f_{i}$表示在题中条件下,还满足$\forall i\le j,a_{j}=a_{i}$的方案数,转移考虑所填的$a_{1}$和$a_{2}$: 1.$a_{1}=1$,此时相当于没有限制,即$f_{i-1}$ 2.$a_{1}>1$且$a_{2}=1$,此时即限制一直到$a_{1}+1$都要是1,接下来任意,即$f_{i-(a_{1}…

A.Infinite Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Consider the infinite sequence of integers: 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5.... The sequence is built in the…

A. Infinite Sequence 题目连接: http://www.codeforces.com/contest/622/problem/A Description Consider the infinite sequence of integers: 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5.... The sequence is built in the following way: at first the number 1 is wr…

题目链接: A. Infinite Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Vasya likes everything infinite. Now he is studying the properties of a sequence s, such that its first element is…

A. Infinite Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Consider the infinite sequence of integers: 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5.... The sequence is built in the…

[arc071f]Infinite Sequence(动态规划) 题面 atcoder 洛谷 题解 不难发现如果两个不为\(1\)的数连在一起,那么后面所有数都必须相等. 设\(f[i]\)表示\([i,n]\)的填法数,初值\(f[n]=n,f[n-1]=n*n\) 考虑转移, 首先可以这里填上一个大于\(1\)的数然后后面连续若干个\(1\),这一部分的方案数是\(\sum_{j=i+3}^n f[j]\),这个后缀和记录一下就好了,然而还漏了一部分,即如果\(i+a_i>n\),那么这里的…

A. Infinite Sequence 题目连接: http://www.codeforces.com/contest/675/problem/A Description Vasya likes everything infinite. Now he is studying the properties of a sequence s, such that its first element is equal to a (s1 = a), and the difference between…

A. Infinite Sequence time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Consider the infinite sequence of integers: 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5.... The sequence is built in the…

Problem description Consider the infinite sequence of integers: 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5.... The sequence is built in the following way: at first the number 1 is written out, then the numbers from 1 to 2, then the numbers from 1 to…

Vasya likes everything infinite. Now he is studying the properties of a sequence s, such that its first element is equal to a (s1 = a), and the difference between any two neighbouring elements is equal to c (si - si - 1 = c). In particular, Vasya won…