1576. Replace All ?’s to Avoid Consecutive Repeating Characters #

Problem #

Given a string s containing only lowercase English letters and the '?' character, convert all the '?' characters into lowercase letters such that the final string does not contain any consecutive repeating characters. You cannot modify the non '?' characters.

It is guaranteed that there are no consecutive repeating characters in the given string except for '?'.

Return the final string after all the conversions (possibly zero) have been made. If there is more than one solution, return any of them. It can be shown that an answer is always possible with the given constraints.

Example 1:

Input: s = "?zs"
Output: "azs"
Explanation: There are 25 solutions for this problem. From "azs" to "yzs", all are valid. Only "z" is an invalid modification as the string will consist of consecutive repeating characters in "zzs".

Example 2:

Input: s = "ubv?w"
Output: "ubvaw"
Explanation: There are 24 solutions for this problem. Only "v" and "w" are invalid modifications as the strings will consist of consecutive repeating characters in "ubvvw" and "ubvww".

Constraints:

• 1 <= s.length <= 100
• s consist of lowercase English letters and '?'.

Problem Summary #

Given a string s containing only lowercase English letters and the ‘?’ character, convert all ‘?’ characters into some lowercase letters so that the final string does not contain any consecutive repeating characters. Note: you cannot modify non-’?’ characters.

The test cases guarantee that, except for the ‘?’ character, there are no consecutive repeating characters. Return the final string after all conversions are completed (possibly with no conversions needed). If there are multiple solutions, return any one of them. It can be proven that under the given constraints, an answer always exists.

Solution Approach #

• Easy problem. Find the positions of the ‘?’ characters in the source string, then replace them one by one with characters from a to z, as long as the replacement character is not the same as the adjacent characters before and after it.

Code #

package leetcode

func modifyString(s string) string {
	res := []byte(s)
	for i, ch := range res {
		if ch == '?' {
			for b := byte('a'); b <= 'z'; b++ {
				if !(i > 0 && res[i-1] == b || i < len(res)-1 && res[i+1] == b) {
					res[i] = b
					break
				}
			}
		}
	}
	return string(res)
}