Problem
Compare two DNA strings position by position and count the differences. Only characters at the same position are compared; do not insert, delete, or shift characters. No biology knowledge is needed.
Implement hamming_distance(first, second).
Input
first: The first DNA string.
second: The equal-length second DNA string.
Output
Return the number of positions with different characters.
Constraints
Both strings have the same length, from 0 to 100,000. Characters are uppercase A, C, G, or T.
Examples
Input:
first = "ACCT"
second = "AGCA"
Expected output:
expected = 2Input:
std::string first = "ACCT";
std::string second = "AGCA";
Expected output:
long long expected = 2;Input:
string first = "ACCT";
string second = "AGCA";
Expected output:
long expected = 2;Explanation
The second position is C versus G and the fourth is T versus A. The first and third match: two differences.
Input:
first = "GATT"
second = "GATT"
Expected output:
expected = 0Input:
std::string first = "GATT";
std::string second = "GATT";
Expected output:
long long expected = 0;Input:
string first = "GATT";
string second = "GATT";
Expected output:
long expected = 0;Explanation
All four positions match, so no differences are counted.
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
Compare both strings one position at a time and count when the characters differ.
Hint 2
A single pass with paired iteration is enough; no rearranging or substring searches are needed.
Hint 3
Remember that equal-length inputs can still be empty, which should yield zero differences.
Expected complexity
O(n) time, O(1) extra space
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.