题解 | #字符个数统计#

const readline = require('readline');

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});
rl.on('line', function (line) {
    const chars = line.split('')
    const results = chars.reduce((prev, cur) => {
        prev[cur] = true
        return prev
    }, {})
    console.log(Object.keys(results).length)
});