Is String Transforms Into Another String easy or hard?

LeetCode classifies this problem as Hard because of the cycle-breaking edge case. The mapping itself is straightforward, but recognizing that a spare character is required to resolve cycles makes the reasoning more subtle than typical hash map problems.

String Transforms Into Another String Python/Java solution

Most implementations use a hash map or dictionary to store the character mapping and a set to track distinct characters in str2. The algorithm iterates once through both strings, validates the mapping, and then checks whether fewer than 26 unique target characters exist to break cycles.

How to solve String Transforms Into Another String in O(n)?

Scan both strings simultaneously and store a mapping from each character in str1 to the corresponding character in str2 using a hash table. If a character maps to two different targets, return false. After building the mapping, check the number of unique characters in str2. If all 26 characters appear and the strings differ, no temporary character exists to break cycles, making the transformation impossible.

What is the best approach for String Transforms Into Another String?

The hash table mapping approach with a free-character check is the most efficient. Iterate through both strings and enforce a consistent mapping from characters in str1 to str2 using a hash map. After building the mapping, verify that str2 uses fewer than 26 unique characters unless the strings are already identical. This ensures cycles can be broken with a temporary character.

Is String Transforms Into Another String asked at Google/Amazon/Meta?

String transformation and character mapping problems appear frequently in interviews at companies like Google, Amazon, and Meta. They test understanding of hash maps, deterministic mappings, and edge cases involving cycles and limited character sets.

What data structure is used in String Transforms Into Another String?

The main data structure is a hash table (hash map) that stores the mapping from characters in str1 to characters in str2. A set is also used to count distinct characters in the target string. These structures allow constant-time lookups and keep the algorithm linear.

What is the time complexity of String Transforms Into Another String?

The optimal solution runs in O(n) time where n is the length of the strings. You perform a single pass to validate character mappings and track distinct characters in the target string. Space complexity is O(1) because the alphabet size is fixed at 26 lowercase letters.

Description Hints 6 Solution Video 4:27

1153. String Transforms Into Another String

Hard34.9% acceptance1 companyPremium elsewhere, free here

Given two strings str1 and str2 of the same length, determine whether you can transform str1 into str2 by doing zero or more conversions.

In one conversion you can convert all occurrences of one character in str1 to any other lowercase English character.

Return true if and only if you can transform str1 into str2.

Example 1:

Input: str1 = "aabcc", str2 = "ccdee"
Output: true
Explanation: Convert 'c' to 'e' then 'b' to 'd' then 'a' to 'c'. Note that the order of conversions matter.

Example 2:

Input: str1 = "leetcode", str2 = "codeleet"
Output: false
Explanation: There is no way to transform str1 to str2.

Constraints:

1 <= str1.length == str2.length <= 10⁴
str1 and str2 contain only lowercase English letters.

Asked at 1 company

Google

Topics

Hash Table String

Hints open one at a time

Hint 1

Model the problem as a graph problem. Add an edge from one character to another if you need to convert between them.

Hint 2

What if one character needs to be converted into more than one character?

Hint 3

There would be no solution. Thus, every node can have at most one outgoing edge.

Hint 4

How to process a linked list?

Hint 5

How to process a cycle?

Hint 6

What if there is a character with no outgoing edge? You can use it to break all cycles!

4:27

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1class Solution:
  def solve(self):
      pass


Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

"aabcc"
"ccdee"

Input

"leetcode"
"codeleet"

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