771. Jewels and Stones

Easy
​
You're given strings jewels representing the types of stones that are jewels, and stones representing the stones you have. Each character in stones is a type of stone you have. You want to know how many of the stones you have are also jewels.
Letters are case sensitive, so "a" is considered a different type of stone from "A".
Example 1:
Input: jewels = "aA", stones = "aAAbbbb"
Output:
3
Example 2:
Input: jewels = "z", stones = "ZZ"
Output:
0
Constraints:
  • 1 <= jewels.length, stones.length <= 50
  • jewels and stones consist of only English letters.
  • All the characters of jewels are unique.

解題

Runtime: 0 ms, faster than 100.00%
Memory Usage: 2.1 MB, less than 55.71%
func numJewelsInStones(jewels string, stones string) int {
m := make(map[byte]bool)
for i:=0; i<len(jewels); i++ {
m[jewels[i]] = true
}
ans := 0
for i:=0; i<len(stones); i++ {
if m[stones[i]] { ans++ }
}
return ans
}