Codeforces 798A - Mike and palindrome

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.

Example
Input
abccaa
Output
YES
Input
abbcca
Output
NO
Input
abcda
Output
YES

思路：题目要求必须改掉一个字母使字符串变为回文字，应注意的有两点：1.只要不一样的字母有一处输出“YES” 2.字符串长度是奇数，并且是回文字的也符合要求， 因为可以修改中间的字母， 仍是一个回文字。 其余的均为“NO”。

#include<stdio.h>
#include<string.h>
int main(){
char str[20];
int cnt=0, i, j, l;

gets(str);
l = strlen(str);
for(i=0, j=l-1; i<j; i++, j--){
if(str[i]!=str[j])cnt++;
}
if(cnt==1)
printf("YES\n");
else if((l&1)==1 && cnt==0)
printf("YES\n");
else 
printf("NO\n");
return 0;
}