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
Example 1
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.
Example 2
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.
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.