G- 3- palindrome

In the beginning of the new year Keivan decided to reverse his name. He doesn’t like palindromes, so he changed Naviek to Navick.

He is too selfish, so for a given n he wants to obtain a string of n characters, each of which is either ‘a’, ‘b’ or ‘c’, with no palindromes of length 3 appearing in the string as a substring. For example, the strings “abc” and “abca” suit him, while the string “aba” doesn’t. He also want the number of letters ‘c’ in his string to be as little as possible.

Input
The first line contains single integer n (1 ≤ n ≤ 2·105) — the length of the string.

Output
Print the string that satisfies all the constraints.

If there are multiple answers, print any of them.

Example
Input
2
Output
aa
Input
3
Output
bba
Note
A palindrome is a sequence of characters which reads the same backward and forward.

使用贪心的算法 ，考虑全部先构造成长度为n , 字符串全为‘a’的字符，从左边开始贪心地维护前i个字符串不是回文字符串： 如果ch[i-2]==ch[i] ,就把ch[i]改为‘b’`

#include<bits/stdc++.h>#define INF 0x3f3f3f#define maxn 200100using namespace std;char ans[maxn];int main(){    int n;    scanf("%d",&n);    fill(ans,ans+n,'a');    for(int i=2;i<n;i++)    {        if(ans[i]==ans[i-2])           ans[i]='b';    }    puts(ans);    return 0;}