【LeetCode】Easy: Two Sum

 

Two Sum

https://leetcode.com/problems/two-sum/

自分の回答

Swift Runtime: 12 ms

class Solution {
    func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
        let dic = Dictionary<Int, Int>(uniqueKeysWithValues: nums.enumerated().map{($0, $1)})
        for (i, num) in nums.enumerated() {
            if dic.values.contains(target - num) {
                let j = dic.filter {$0.value == (target - num)}.keys.first!
                return [i,j]
            }
        }
        fatalError()
    }
}

回答例

https://leetcode.com/problems/two-sum/solution/

const twoSum = function(nums, target) {
    const comp = {};
    for(let i=0; i<nums.length; i++){
        if(comp[ nums[i] ] >= 0){
            return [ comp[ nums[i] ] , i]
        }
        comp[ target-nums[i] ] = i
    }
};

回答例を見て修正

class Solution {
    func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
        var dic = Dictionary<Int, Int>()
        for (i, num) in nums.enumerated() {
            if let j = dic[target - num] {
                return [i,j]
            }
            dic[num] = i
        }
        fatalError("No two sum solution")
    }
}

f:id:hira22_1:20200604085655p:plain

感想

  • ヒントを見て、Dictionary を使うとこまではわかった。
  • Dictionaryの Key に与えられた数字を入れていくのは、そういうケースがなかったからか発想できなかった。
  • 回答例を実行すると 0ms で実行されるのだが、もっと早くなるのだろうか…

参考

Swift - SwiftのDictionary型でkeyを取り出す方法｜teratail

let a = [
   "apple": 100,
   "orange": 200,
   "banana": 100,
]
print(Array(a.filter {$0.value == 100}.keys))
//=> ["banana", "apple"]

functional programming - Convert Swift Array to Dictionary with indexes - Stack Overflow

Xcode 9 - 10 • Swift 4.0 - 4.2

Using Swift 4 reduce(into:) method:

extension Collection  {
    var indexedDictionary: [String: Element] {
        return enumerated().reduce(into: [:]) { $0[String($1.offset)] = $1.element }
    }
}

Using Swift 4 Dictionary(uniqueKeysWithValues:) initializer and passing a new array from the enumerated collection:

extension Collection {
    var indexedDictionary: [String: Element] {
        return Dictionary(uniqueKeysWithValues: enumerated().map{(String($0),$1)})
    }
}