iOS Interview - Leetcode 383. Ransom Note

May 16, 2024 • 1 min read • #swift, #interview, #leetcode

Primary idea: Matching character frequencies between 2 string
Time Complexity: O(m + n)
Space Complexity: O(n)

func countCharacterFrequency(_ string: String) -> [Character: Int] {
    var frequencyDict: [Character: Int] = [:]

    for char in string {
        frequencyDict[char, default: 0] += 1
    }

    return frequencyDict
}

func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
    guard magazine.count >= ransomNote.count else { return false }

    var f = countCharacterFrequency(magazine)

    for c in ransomNote {
        if f[c] == nil {
            return false
        }

        if f[c] == 0 {
            return false
        }

        f[c] = f[c]! - 1
    }

    return true
}

canConstruct("a", "b") // false
canConstruct("aa", "ab") // false
canConstruct("aa", "aab") // true