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[1차] 뉴스 클러스터링 #34

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[1차] 뉴스 클러스터링 #34

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42 changes: 42 additions & 0 deletions WEEK03/프로그래머스_[1차] 뉴스 클러스터링/Oliver.swift
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Original file line number Diff line number Diff line change
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func solution(_ str1: String, _ str2: String) -> Int {
let jac = jaccard(str1, str2)
return Int(jac * 65536)
}

// 자카드 유사도
func jaccard(_ s1: String, _ s2: String) -> Double {
let set1 = makeSet(s1)
var set2 = makeSet(s2)

if set1.isEmpty && set2.isEmpty { return 1.0 }

var intersection: [String] = []
var unionCount: Int = 0

for element in set1 {
if let idx = set2.firstIndex(of: element) {
intersection.append(element)
set2.remove(at: idx)
}
}

unionCount = set1.count + set2.count
return Double(intersection.count) / Double(unionCount)
}
Comment on lines +7 to +25
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@gemini-code-assist gemini-code-assist bot Feb 5, 2026

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high

jaccard 함수에서 교집합과 합집합을 계산하는 현재 방식은 배열에 대해 firstIndex(of:)와 remove(at:)를 반복적으로 사용합니다. 이 배열 연산은 최악의 경우 O(N*M)의 시간 복잡도를 가질 수 있어, 입력 크기가 커질수록 성능 저하가 발생할 수 있습니다.
makeSet 함수에서 반환하는 딕셔너리(다중집합)를 활용하면, 교집합과 합집합을 O(N+M) 시간 복잡도로 효율적으로 계산할 수 있습니다. 제안된 코드는 다중집합의 합집합 공식인 |A ∪ B| = |A| + |B| - |A ∩ B|를 사용합니다.

func jaccard(_ s1: String, _ s2: String) -> Double {
    let multiset1 = makeSet(s1)
    let multiset2 = makeSet(s2)

    if multiset1.isEmpty && multiset2.isEmpty { return 1.0 }

    var intersectionCount = 0

    // 교집합 계산
    for (bigram, count1) in multiset1 {
        if let count2 = multiset2[bigram] {
            intersectionCount += min(count1, count2)
        }
    }

    // 합집합 계산: |A U B| = |A| + |B| - |A intersect B|
    let sumOfCounts1 = multiset1.values.reduce(0, +)
    let sumOfCounts2 = multiset2.values.reduce(0, +)
    let unionCount = sumOfCounts1 + sumOfCounts2 - intersectionCount

    // unionCount가 0인 경우 (두 다중집합 모두 비어있거나, 교집합이 전체를 상쇄하는 경우 등)
    if unionCount == 0 { return 1.0 }

    return Double(intersectionCount) / Double(unionCount)
}


// 집합 만들기
func makeSet(_ string: String) -> [String] {
let chars = Array(string.lowercased())
var result: [String] = []

for i in 0..<chars.count-1 {
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security-medium medium

The makeSet function has a potential Denial of Service (DoS) vulnerability. If an empty string is passed, the range 0..<chars.count-1 becomes 0..<-1, causing a runtime crash in Swift. A robust implementation should handle empty inputs to prevent this. Additionally, for better performance and clearer multiset representation, consider changing makeSet to return a dictionary [String: Int] to store bigram counts, which would also improve the efficiency of jaccard function calculations.

Suggested change
for i in 0..<chars.count-1 {
for i in 0..<max(0, chars.count - 1) {

let c1 = chars[i]
let c2 = chars[i+1]

if c1.isLetter && c2.isLetter {
result.append(String([c1, c2]))
}
}

return result
}