题解 | #计算某字母出现次数#

用一个数组存放即可，数组 + 正则

let arr = [];
while(line = readline()) {
    arr.push(line)
}
let s = arr[0];
let index = arr[1];
const letterCount = new Array(26).fill(0);
let len = s.length;
for (let i = 0; i < len; i += 1) {
    if (/[A-Z]/.test(s[i])) {
        letterCount[s.charCodeAt(i) - 'A'.charCodeAt(0)] += 1;
    }
    if (/[a-z]/.test(s[i])) {
        letterCount[s.charCodeAt(i) - 'a'.charCodeAt(0)] += 1;
    }
}
console.log(/[a-z]/.test(index) ? letterCount[index.charCodeAt(0) - 'a'.charCodeAt(0)] : letterCount[index.charCodeAt(0) - 'A'.charCodeAt(0)])