3. 构成指定长度字符串的个数

const readline = require('readline');
const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
});

function generateDistingctStrings(str, length, current, set, used) {
    if (current.length === length) {
        set.add(current);
        return;
    }
    for(let i=0; i<str.length; i++) {
        if (used[i] || str[i] === current[current.length - 1]) {
            continue;
        }
        used[i] = true;
        generateDistingctStrings(str, length, current + str[i], set, used);
        used[i] = false;
    }
}

function contDistinctStrings(str, length) {
    let set = new Set();
    let used = [];
    generateDistinctStrings(str, length, '', set, used);
    return set.size;
}


rl.on('line', (input) => {
    const parts = input.split(' ');
    const str = parts[0];
    const length = parseInt(parts[1]);
    const count = contDistinctStrings(str, length);
    console.log(count);
    rl.close();
})