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9.9 EMB 奖励。
单点时限: 2.0 sec
内存限制: 256 MB
We consider sequences of letters. We say a sequence x1x2…xn contains a stammer, if we can find in it two occurrences of the same subsequence, one directly following the other, i.e. if for some i and j (1 <= i < j <= (n+i+1)/2) we have xi = xj, xi+1 = xj+1, …, xj-1 = x2j-i-1.
We are interested in n-element sequences having no stammers, built of the minimal number of different letters.
Example
For n = 3 it is enough to use two letters, say a and b. We have exactly two 3-element sequences without stammers build of those letters: aba and bab. For n = 5 we need three different letters. For example abcab is a three-letter sequence without stammers. In the sequence babab we have two stammers: ba and ab.
Task
Write a program which:
reads the length of the sequence n,
computes an n-element sequence with no stammers built of the minimal number of different letters,
writes the result.
In the first line of the standard input there is one positive integer n, 1 <= n <= 10000000.
Your program should write to the standard output. In the first line there should be one positive integer k equal to the minimal number of different letters that must appear in an n-element sequence having no stammers.
In the second line one should write the computed sequence without stammers as a word that comprises n lower case letters of English alphabet and is built only of the letters from a up to the k-th letter of the alphabet. If there are many such sequences, your program should write one of them.
You may assume 26 letters are enough.
5
3 abcab
0 人解决，1 人已尝试。
0 份提交通过，共有 5 份提交。
9.9 EMB 奖励。