2734. Lexicographically Smallest String After Substring Operation 

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
class Solution {
    public String smallestString(String s) {        
        char[] chars = s.toCharArray();
        boolean replaced = false;
        for (int i = 0; i < chars.length; i++) {
            if (chars[i] == 'a') {
                if (replaced) {
                    break;
                }
            } else {
                chars[i]--;
                replaced = true;
            }
        }

        if (!replaced) {
            // 注意必须替换一次，且 a 可以被替换为 z
            chars[chars.length - 1] = 'z';
        }

        return new String(chars);
    }
}

Reference

2734. Lexicographically Smallest String After Substring Operation