LeetCode: 771. Jewels and Stones/ 珠宝和宝石

You're given strings J representing the types of stones that are jewels, and S representing the stones you have. Each character in S is a type of stone you have. You want to know how many of the stones you have are also jewels.

The letters in J are guaranteed distinct, and all characters in J and S are letters. Letters are case sensitive, so "a" is considered a different type of stone from "A".

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理解一下:
J和S都是字符串(char数组).
S中包含多少个J所包含的单个字符(char)
需要区分大小写

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  例子:
  Input: J = "aA", S = "aAAbbbb"
  Output: 3

  例子:
  Input: J = "z", S = "ZZ"
  Output: 0

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Note:

S and J will consist of letters and have length at most 50.
The characters in J are distinct.
翻译: J最大长度为50. J.length <= 50

我的答案

class Solution {
    func numJewelsInStones(_ J: String, _ S: String) -> Int {
        var count = 0
        var j_dic = [Character: Int]()
        for (offset , element) in J.enumerated() {
            j_dic[element] = offset
        }
        for (_, element) in S.enumerated() {
            if let _ = j_dic[element] {
                count += 1
            }
        }
        return count
    }
}

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