Jewels and Stones


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


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


Maintain a hash map of all jewels, check each stone against the map, to see if it is a jewel, increase the count if it is. Runs in O(n) time.

func numJewelsInStones(J string, S string) int {
    result := 0
    if len(J)==0{ return result }
    jmap := make(map[rune]bool, 0)
    for _, ch := range J{
        if !jmap[ch]{
            jmap[ch] = true
    for _, ch := range S{
        if jmap[ch]{
    return result