Check If String Is Transformable With Substring Sort Operations

Given two strings s and t, we want to determine if it is possible to transform s into t by sorting non-empty substrings in ascending order.


The key to this problem is understanding that a character can only move to the left during the transformations. If the target string t requires a character to move right compared to its original position in string s, it will be impossible to reach t.


  1. Check Frequencies: The frequencies of characters in s and t should be the same. If not, return false.

  2. Build Position Queue: For each digit (0-9), build a queue containing the positions of that digit in s. This helps in tracking where the digits can move.

  3. Iterate Through Target: Iterate through t and for each character, pop from the corresponding queue. Ensure that there are no digits smaller than the current digit to its left in the original string s.


from collections import deque

class Solution:
    def isTransformable(self, s: str, t: str) -> bool:
        # Step 1: Check if the frequency of characters in s and t are the same
        if sorted(s) != sorted(t):
            return False

        # Step 2: Build position queues
        pos_queues = [deque() for _ in range(10)]
        for i, ch in enumerate(s):

        # Step 3: Iterate through t
        for ch in t:
            digit = int(ch)
            if not pos_queues[digit]:
                return False

            # Check if there are smaller digits to the left of the current digit
            for smaller_digit in range(digit):
                if pos_queues[smaller_digit] and pos_queues[smaller_digit][0] < pos_queues[digit][0]:
                    return False


        return True

Key Takeaways

  • Keep track of the original positions of the digits in s.
  • Understand that the transformation only allows moving the characters to the left.

Complexity Analysis

  • Time complexity: (O(n)), where (n) is the length of the strings s and t. The operations inside the loop are (O(1)), and the loop iterates (n) times.
  • Space complexity: (O(n)), as we use queues to store the positions of the digits in s.

You can practice a series of problems related to arrays, strings, and sorting to familiarize yourself with the concepts needed for problem 1585.

Here’s a list of 10 problems:

  1. LeetCode 344. Reverse String

    • In this problem, you need to reverse the characters in a string. This will help you understand basic string manipulations.
  2. LeetCode 242. Valid Anagram

    • This problem deals with checking whether two strings are anagrams or not. It will help you understand character frequency counting, which could be helpful.
  3. LeetCode 937. Reorder Data in Log Files

    • This problem focuses on sorting a list of strings based on certain conditions. It’ll help you understand sorting with custom comparison function.
  4. LeetCode 215. Kth Largest Element in an Array

    • This problem will teach you how to find the Kth largest element in an array using sorting and partitioning techniques.
  5. LeetCode 75. Sort Colors

    • This problem helps you understand in-place sorting and will strengthen your understanding of sorting algorithms.
  6. LeetCode 350. Intersection of Two Arrays II

    • It is a problem about finding the intersection of two arrays, which will help you better understand how to operate with arrays and deal with their elements.
  7. LeetCode 3. Longest Substring Without Repeating Characters

    • This problem requires you to find the longest substring without repeating characters. It’ll help you get used to string manipulations and sliding window concepts.
  8. LeetCode 451. Sort Characters By Frequency

    • This problem requires you to sort characters in a string based on their frequency. It’ll help you understand how to apply sorting based on conditions.
  9. LeetCode 88. Merge Sorted Array

    • This problem will help you learn how to merge two sorted arrays, a fundamental operation in many sorting algorithms like merge sort.
  10. LeetCode 283. Move Zeroes

    • This problem is about moving all the 0’s to the end of an array while maintaining the relative order of the non-zero elements. It will help you understand in-place array operations and the concept of maintaining relative order, which is quite important for problem 1585.

Problem Classification

Problem Statement:Given two strings s and t, transform string s into string t using the following operation any number of times:

Choose a non-empty substring in s and sort it in place so the characters are in ascending order. For example, applying the operation on the underlined substring in “14234” results in “12344”. Return true if it is possible to transform s into t. Otherwise, return false.

A substring is a contiguous sequence of characters within a string.

Example 1:

Input: s = “84532”, t = “34852” Output: true Explanation: You can transform s into t using the following sort operations: “84532” (from index 2 to 3) -> “84352” “84352” (from index 0 to 2) -> “34852” Example 2:

Input: s = “34521”, t = “23415” Output: true Explanation: You can transform s into t using the following sort operations: “34521” -> “23451” “23451” -> “23415” Example 3:

Input: s = “12345”, t = “12435” Output: false


s.length == t.length 1 <= s.length <= 105 s and t consist of only digits.

Analyze the provided problem statement. Categorize it based on its domain, ignoring ‘How’ it might be solved. Identify and list out the ‘What’ components. Based on these, further classify the problem. Explain your categorizations.

Visual Model of the Problem

How to visualize the problem statement for this problem?

Problem Restatement

Could you start by paraphrasing the problem statement in your own words? Try to distill the problem into its essential elements and make sure to clarify the requirements and constraints. This exercise should aid in understanding the problem better and aligning our thought process before jumping into solving it.

Abstract Representation of the Problem

Could you help me formulate an abstract representation of this problem?

Given this problem, how can we describe it in an abstract way that emphasizes the structure and key elements, without the specific real-world details?


Are there any specialized terms, jargon, or technical concepts that are crucial to understanding this problem or solution? Could you define them and explain their role within the context of this problem?

Problem Simplification and Explanation

Could you please break down this problem into simpler terms? What are the key concepts involved and how do they interact? Can you also provide a metaphor or analogy to help me understand the problem better?


Given the problem statement and the constraints provided, identify specific characteristics or conditions that can be exploited to our advantage in finding an efficient solution. Look for patterns or specific numerical ranges that could be useful in manipulating or interpreting the data.

What are the key insights from analyzing the constraints?

Case Analysis

Could you please provide additional examples or test cases that cover a wider range of the input space, including edge and boundary conditions? In doing so, could you also analyze each example to highlight different aspects of the problem, key constraints and potential pitfalls, as well as the reasoning behind the expected output for each case? This should help in generating key insights about the problem and ensuring the solution is robust and handles all possible scenarios.

Identification of Applicable Theoretical Concepts

Can you identify any mathematical or algorithmic concepts or properties that can be applied to simplify the problem or make it more manageable? Think about the nature of the operations or manipulations required by the problem statement. Are there existing theories, metrics, or methodologies in mathematics, computer science, or related fields that can be applied to calculate, measure, or perform these operations more effectively or efficiently?

Problem Breakdown and Solution Methodology

Given the problem statement, can you explain in detail how you would approach solving it? Please break down the process into smaller steps, illustrating how each step contributes to the overall solution. If applicable, consider using metaphors, analogies, or visual representations to make your explanation more intuitive. After explaining the process, can you also discuss how specific operations or changes in the problem’s parameters would affect the solution? Lastly, demonstrate the workings of your approach using one or more example cases.

Inference of Problem-Solving Approach from the Problem Statement

How did you infer from the problem statement that this problem can be solved using ?

Stepwise Refinement

  1. Could you please provide a stepwise refinement of our approach to solving this problem?

  2. How can we take the high-level solution approach and distill it into more granular, actionable steps?

  3. Could you identify any parts of the problem that can be solved independently?

  4. Are there any repeatable patterns within our solution?

Solution Approach and Analysis

Given the problem statement, can you explain in detail how you would approach solving it? Please break down the process into smaller steps, illustrating how each step contributes to the overall solution. If applicable, consider using metaphors, analogies, or visual representations to make your explanation more intuitive. After explaining the process, can you also discuss how specific operations or changes in the problem’s parameters would affect the solution? Lastly, demonstrate the workings of your approach using one or more example cases.

Thought Process

Explain the thought process by thinking step by step to solve this problem from the problem statement and code the final solution. Write code in Python3. What are the cues in the problem statement? What direction does it suggest in the approach to the problem? Generate insights about the problem statement.

From Brute Force to Optimal Solution

Could you please begin by illustrating a brute force solution for this problem? After detailing and discussing the inefficiencies of the brute force approach, could you then guide us through the process of optimizing this solution? Please explain each step towards optimization, discussing the reasoning behind each decision made, and how it improves upon the previous solution. Also, could you show how these optimizations impact the time and space complexity of our solution?

Coding Constructs

Consider the following piece of complex software code.

  1. What are the high-level problem-solving strategies or techniques being used by this code?

  2. If you had to explain the purpose of this code to a non-programmer, what would you say?

  3. Can you identify the logical elements or constructs used in this code, independent of any programming language?

  4. Could you describe the algorithmic approach used by this code in plain English?

  5. What are the key steps or operations this code is performing on the input data, and why?

  6. Can you identify the algorithmic patterns or strategies used by this code, irrespective of the specific programming language syntax?

Language Agnostic Coding Drills

Your mission is to deconstruct this code into the smallest possible learning units, each corresponding to a separate coding concept. Consider these concepts as unique coding drills that can be individually implemented and later assembled into the final solution.

  1. Dissect the code and identify each distinct concept it contains. Remember, this process should be language-agnostic and generally applicable to most modern programming languages.

  2. Once you’ve identified these coding concepts or drills, list them out in order of increasing difficulty. Provide a brief description of each concept and why it is classified at its particular difficulty level.

  3. Next, describe the problem-solving approach that would lead from the problem statement to the final solution. Think about how each of these coding drills contributes to the overall solution. Elucidate the step-by-step process involved in using these drills to solve the problem. Please refrain from writing any actual code; we’re focusing on understanding the process and strategy.

Targeted Drills in Python

Now that you’ve identified and ordered the coding concepts from a complex software code in the previous exercise, let’s focus on creating Python-based coding drills for each of those concepts.

  1. Begin by writing a separate piece of Python code that encapsulates each identified concept. These individual drills should illustrate how to implement each concept in Python. Please ensure that these are suitable even for those with a basic understanding of Python.

  2. In addition to the general concepts, identify and write coding drills for any problem-specific concepts that might be needed to create a solution. Describe why these drills are essential for our problem.

  3. Once all drills have been coded, describe how these pieces can be integrated together in the right order to solve the initial problem. Each drill should contribute to building up to the final solution.

Remember, the goal is to not only to write these drills but also to ensure that they can be cohesively assembled into one comprehensive solution.


Similar Problems

Given the problem , identify and list down 10 similar problems on LeetCode. These should cover similar concepts or require similar problem-solving approaches as the provided problem. Please also give a brief reason as to why you think each problem is similar to the given problem.