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export default class HintKeyProducer {
private charset: string;
private counter: number[];
constructor(charset: string) {
if (charset.length === 0) {
throw new TypeError('charset is empty');
}
this.charset = charset;
this.counter = [];
}
produce(): string {
this.increment();
return this.counter.map(x => this.charset[x]).join('');
}
private increment(): void {
let max = this.charset.length - 1;
if (this.counter.every(x => x === max)) {
this.counter = new Array(this.counter.length + 1).fill(0);
return;
}
this.counter.reverse();
let len = this.charset.length;
let num = this.counter.reduce((x, y, index) => x + y * len ** index) + 1;
for (let i = 0; i < this.counter.length; ++i) {
this.counter[i] = num % len;
num = ~~(num / len);
}
this.counter.reverse();
}
}
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