A. Mike and palindrome

Codeforces

IDCF798A

Time2000ms

Memory256MB

Difficulty—

brute forceconstructive algorithmsstrings

English · Original

Chinese · Translation

Formal · Original

Mike has a string _s_ consisting of only lowercase English letters. He wants to **change exactly one** character from the string so that the resulting one is a palindrome. A palindrome is a string that reads the same backward as forward, for example strings "_z_", "_aaa_", "_aba_", "_abccba_" are palindromes, but strings "_codeforces_", "_reality_", "_ab_" are not. ## Input The first and single line contains string _s_ (1 ≤ |_s_| ≤ 15). ## Output Print "_YES_" (without quotes) if Mike can change **exactly** one character so that the resulting string is palindrome or "_NO_" (without quotes) otherwise. [samples]

Mike 有一个仅由小写英文字母组成的字符串 #cf_span[s]。他希望将字符串中的*恰好一个*字符进行修改，使得修改后的字符串成为回文串。回文串是指正读和反读都相同的字符串，例如字符串 "_z_"、"_aaa_"、"_aba_"、"_abccba_" 是回文串，但字符串 "_codeforces_"、"_reality_"、"_ab_" 不是。第一行且仅有一行包含字符串 #cf_span[s]（#cf_span[1 ≤ |s| ≤ 15]）。如果 Mike 能够通过修改*恰好一个*字符使结果字符串成为回文串，则输出 "_YES_"（不含引号）；否则输出 "_NO_"（不含引号）。 ## Input 第一行且仅有一行包含字符串 #cf_span[s]（#cf_span[1 ≤ |s| ≤ 15]）。 ## Output 如果 Mike 能够通过修改*恰好一个*字符使结果字符串成为回文串，则输出 "_YES_"（不含引号）；否则输出 "_NO_"（不含引号）。 [samples]

**Definitions** Let $ s \in \Sigma^* $ be a string of length $ n $, where $ \Sigma = \{a, b, \dots, z\} $ and $ 1 \leq n \leq 15 $. **Constraints** 1. $ |s| = n $, with $ 1 \leq n \leq 15 $ 2. Each character of $ s $ is a lowercase English letter. **Objective** Determine whether there exists exactly one index $ i \in \{1, \dots, n\} $ and a character $ c \in \Sigma $ such that replacing $ s[i] $ with $ c $ yields a palindrome, and the resulting string is not identical to $ s $. Equivalently, define $ s' $ such that $ s'[j] = s[j] $ for all $ j \neq i $, and $ s'[i] = c \neq s[i] $, and $ s' $ is a palindrome. Output "YES" if such $ i $ and $ c $ exist; otherwise, output "NO".

Samples

Input #1

abccaa

Output #1

YES

Input #2

abbcca

Output #2

NO

Input #3

abcda

Output #3

YES

API Response (JSON)

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