771. Jewels and Stones #

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.

Problem Summary #

Given string J representing the types of stones that are jewels, and string S representing the stones you have. Each character in S represents a type of stone you have. You want to know how many of the stones you have are jewels.

The letters in J are not repeated, and all characters in J and S are letters. Letters are case sensitive, so “a” and “A” are different types of stones.

Solution Approach #

• Given 2 strings, find the number of characters in string S that appear in string J. This is an easy problem.

Code #

package leetcode

import "strings"

// Solution 1
func numJewelsInStones(J string, S string) int {
	count := 0
	for i := range S {
		if strings.Contains(J, string(S[i])) {
			count++
		}
	}
	return count
}

// Solution 2
func numJewelsInStones1(J string, S string) int {
	cache, result := make(map[rune]bool), 0
	for _, r := range J {
		cache[r] = true
	}
	for _, r := range S {
		if _, ok := cache[r]; ok {
			result++
		}
	}
	return result
}