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Model the problem as a graph problem. Add an edge from one character to another if you need to convert between them.
What if one character needs to be converted into more than one character?
There would be no solution. Thus, every node can have at most one outgoing edge.
How to process a linked list?
How to process a cycle?
What if there is a character with no outgoing edge? You can use it to break all cycles!
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Cycles occur when characters map to each other, such as a → b and b → a. Breaking such cycles requires a temporary unused character; if all 26 letters are already used in the target string, the transformation becomes impossible.
Yes, this problem tests understanding of hash maps, character mapping, and edge cases involving cycles. Variations of this concept can appear in interviews at large tech companies and competitive programming platforms.
A hash table (or dictionary) is ideal for tracking mappings between characters of the two strings. It allows constant-time checks to ensure each character maps consistently throughout the transformation.
The optimal approach uses a hash map to enforce consistent character mappings from the first string to the second. After validating mappings, check the number of unique characters in the target string to determine whether cycles can be broken.