May Leetcode Challenge - Day 2

HàPQ -

Problem

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.

Example 1:

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

Example 2:

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

Note:

  • S and J will consist of letters and have length at most 50.
  • The characters in J are distinct.

Solution

Convert the list of jewels J to hash table, then iterate through S, lookup in hash-table with O(n) time.

class Solution {
    func numJewelsInStones(_ J: String, _ S: String) -> Int {
        let searchTable = Set(Array(J))
        var res = 0
        for s in S {
            if searchTable.contains(s) { res += 1 }
        }
        return res
    }
}