Lexicographically Smallest String After Substring Operation — LeetCode 2734 Python Solution

MediumGreedyString

Problem: #2734
Pattern: Greedy
Reading time: 2 min
Source: leetcode.com

The problem

Given a string s consisting of lowercase English letters. Perform the following operation: Select any non-empty substring then replace every letter of the substring with the preceding letter of the English alphabet.

Python solution

Python

class Solution:
    def smallestString(self, s: str) -> str:
        n = len(s)
        i = 0
        while i < n and s[i] == "a":
            i += 1
        if i == n:
            return s[:-1] + "z"
        j = i
        while j < n and s[j] != "a":
            j += 1
        return s[:i] + "".join(chr(ord(c) - 1) for c in s[i:j]) + s[j:]

Complexity

Measure	Complexity
Time	O(n)
Space	O(n) auxiliary

Pattern: Greedy

Take the locally best option every time — when you can prove that never costs you later. LeetCode 2734. Lexicographically Smallest String After Substring Operation is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Greedy.

The greedy guide has the Python template for the pattern and the 346 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 2734. Lexicographically Smallest String After Substring Operation?: LeetCode 2734. Lexicographically Smallest String After Substring Operation is rated Medium on LeetCode.
What is the time complexity of LeetCode 2734. Lexicographically Smallest String After Substring Operation?: The Python solution on this page runs in O(n).
What is the space complexity of LeetCode 2734. Lexicographically Smallest String After Substring Operation?: The Python solution on this page uses O(n) auxiliary space.
What topics does LeetCode 2734. Lexicographically Smallest String After Substring Operation cover?: LeetCode 2734. Lexicographically Smallest String After Substring Operation is tagged Greedy and String on LeetCode.