1328. Break a Palindrome

Medium

Given a palindromic string of lowercase English letters palindrome, replace exactly one character with any lowercase English letter so that the resulting string is not a palindrome and that it is the lexicographically smallest one possible.

Return the resulting string. If there is no way to replace a character to make it not a palindrome, return an empty string.

A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ, a has a character strictly smaller than the corresponding character in b. For example, "abcc" is lexicographically smaller than "abcd" because the first position they differ is at the fourth character, and 'c' is smaller than 'd'.

Example 1:

Input: palindrome = "abccba"
Output:
 "aaccba"
Explanation:
 There are many ways to make "abccba" not a palindrome, such as "zbccba", "aaccba", and "abacba".
Of all the ways, "aaccba" is the lexicographically smallest.

Example 2:

Input: palindrome = "a"
Output:
 ""
Explanation:
 There is no way to replace a single character to make "a" not a palindrome, so return an empty string.

Constraints:

• 1 <= palindrome.length <= 1000

• palindrome consists of only lowercase English letters.

解題

1. 如果字串長度小於等於一，不論如何一定是palindrome，所以回傳""

2. 迭代到字串的一半，若是遇到不等於a的字元，將之改為a

3. 若全部都等於a，將最後一個字元改為b

func breakPalindrome(palindrome string) string {
    ans := []rune(palindrome)
    length := len(palindrome)

	if length <= 1 {
		return ""
	}

	for i := 0; i < length/2; i++ {
		if ans[i] != 'a' {
			ans[i] = 'a'
			return string(ans)
		}
	}

	ans[length-1] = 'b'
	return string(ans)
}