Build the next version of the Unix sort command, this time with the -k flag baked in. Each input line is comma-separated and is guaranteed to have at least field fields (a field may be empty, as in "a,,c"). Given a 1-indexed field number, sort the lines stably by the value at that field, compared as strings by character code, and return the original lines joined by newlines (\n). Lines whose fields are equal keep their original relative order. This matches the real command sort -t, -k N,N -s in the C locale. If the list is empty, return the empty string.
Function signature:
func sortLines(_ lines: [String], _ field: Int) -> String
Example:
Input: field = 2, lines = ["alice,30", "bob,25", "carol,40"] Output: "bob,25\nalice,30\ncarol,40" When printed: bob,25 alice,30 carol,40
Swift's
sort(by:) is a stable sort. Make a mutable copy of lines, then sort it with a comparator that splits each line on "," and compares the entry at field - 1.
The full solution:
class Solution {
func sortLines(_ lines: [String], _ field: Int) -> String {
var sortedLines = lines
sortedLines.sort { $0.split(separator: ",", omittingEmptySubsequences: false)[field - 1] < $1.split(separator: ",", omittingEmptySubsequences: false)[field - 1] }
return sortedLines.joined(separator: "\n")
}
}
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