L771.java

class Solution771 {
    class Solution {
        /**
         * 771. Jewels and Stones https://leetcode.com/problems/jewels-and-stones/description/
         *
         * @param J Jewel string
         * @param S Stone string
         * @return Number of stones which are jewels
         * @timeComplexity O(max ( j, s)) where j is number of jewels and s is number of stones
         * @spaceComplexity O(1) Using a boolean array of fixed size i.e. 52
         */
        public int numJewelsInStones(String J, String S) {
            boolean[] isJewel = new boolean[52];
            for (char c : J.toCharArray()) {
                if (c <= 'Z') {
                    // We record whether a capital letter is jewel from 0-25
                    isJewel[c - 'A'] = true;
                } else if (c <= 'z') {
                    // We record whether a small letter is jewel from 26-51
                    isJewel[c - 'a' + 26] = true;
                }
            }
            int count = 0;
            for (char c : S.toCharArray()) {
                if (c <= 'Z') {
                    if (isJewel[c - 'A']) {
                        count++;
                    }
                } else if (c <= 'z') {
                    if (isJewel[c - 'a' + 26]) {
                        count++;
                    }
                }
            }
            return count;
        }
    }
}