Problem
Build an RNA string by replacing every DNA character with its partner. Use this complete mapping: A → U, C → G, G → C, T → A. Preserve the original order. No biology knowledge is needed.
Implement dna_to_rna(dna).
Input
dna: The DNA string to transform.
Output
Return the transformed string. Empty input returns an empty string.
Constraints
0 ≤ DNA length ≤ 100,000. Characters are uppercase A, C, G, or T.
Examples
Input:
dna = "ACGT"
Expected output:
expected = "UGCA"Input:
std::string dna = "ACGT";
Expected output:
std::string expected = "UGCA";Input:
string dna = "ACGT";
Expected output:
string expected = "UGCA";Explanation
A becomes U, C becomes G, G becomes C, and T becomes A, giving UGCA.
Input:
dna = ""
Expected output:
expected = ""Input:
std::string dna = "";
Expected output:
std::string expected = "";Input:
string dna = "";
Expected output:
string expected = "";Explanation
There are no characters to replace, so the result is empty.
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
Each DNA letter maps to exactly one RNA letter, so translate character by character.
Hint 2
Use a direct lookup for the four valid symbols while preserving the original order.
Hint 3
An empty input should return an empty string, and every character is guaranteed to be valid.
Expected complexity
O(n) time, O(n) extra space
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.