Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 23

Description

Break a Palindrome

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.

Example 3:

Input: palindrome = "aa"
Output: "ab"

Example 4:

Input: palindrome = "aba"
Output: "abb"

Constraints:

• 1 <= palindrome.length <= 1000
• palindrome consists of only lowercase English letters.

Solution

class Solution {
public:
  string breakPalindrome(string palindrome) {
    int len = palindrome.length();
    if(len == 1) return "";
    for(int i = 0; i * 2 + 1 < len; ++i) {
      if(palindrome[i] != 'a') {
        palindrome[i] = 'a';
        return palindrome;
      }
    }
    palindrome.back() = 'b';
    return palindrome;
  }
};

// Accepted
// 30/30 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 45.58 % of cpp submissions (6.2 MB)