2 seconds
256 megabytes
standard input
standard output
Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7.
For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are
not.
Petya recently learned to determine whether a string of lowercase Latin letters is lucky. For each individual letter all its positions in the string are written out in the increasing order. This results in 26 lists
of numbers; some of them can be empty. A string is considered lucky if and only if in each list the absolute difference of any two adjacent numbers is a lucky number.
For example, let's consider string "zbcdzefdzc". The lists of positions of equal letters are:
..., y are empty.
This string is lucky as all differences are lucky numbers. For letters z: 5 - 1 = 4, 9 - 5 = 4,
for letters c: 10 - 3 = 7, for
lettersd: 8 - 4 = 4.
Note that if some letter occurs only once in a string, it doesn't influence the string's luckiness after building the lists of positions of equal letters. The string where all the letters are distinct is considered lucky.
Find the lexicographically minimal lucky string whose length equals n.
The single line contains a positive integer n (1 ≤ n ≤ 105)
— the length of the sought string.
Print on the single line the lexicographically minimal lucky string whose length equals n.
5
abcda
3
abc
The lexical comparison of strings is performed by the < operator in modern programming languages. String a is lexicographically less than
string b if exists such i (1 ≤ i ≤ n),
that ai < bi,
and for any j (1 ≤ j < i) aj = bj.
解题说明：此题就是要求相同的字母出现的顺序之差为4,7这样的幸运数，简单的做法是每隔4个位置安插一个相同的字母，只用a,b,c,d这四个字母即可。
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <string>
#include<set>
#include <algorithm>
using namespace std;
int main()
{
int n,j,counter=0;
scanf("%d",&n);
for(j=1;j<=n;j++)
{
printf("%c",'a'+counter);
counter=(counter+1)%4;
}
return 0;
}