iteragain/dist/esm/internal/PermutationsIterator.js

Javascript Iterable/Iterator/Generator-function utilities.

import RangeIterator from './RangeIterator';
import toArray from '../toArray';
/** Returns all successive `size` length permutations of the input `iterator`. */
export class PermutationsIterator {
    constructor(iterator, size) {
        this.started = false;
        this.pool = toArray(iterator);
        this.size = size !== null && size !== void 0 ? size : this.pool.length;
        if (this.size > this.pool.length)
            this.next = () => ({ done: true, value: undefined });
        this.indices = toArray(new RangeIterator(0, this.pool.length));
        this.cycles = toArray(new RangeIterator(this.pool.length, this.pool.length - this.size, -1));
    }
    get value() {
        return this.indices.slice(0, this.size).map(i => this.pool[i]);
    }
    [Symbol.iterator]() {
        return this;
    }
    next() {
        if (!this.started) {
            this.started = true;
            return { done: false, value: this.value };
        }
        for (let i = this.size - 1; i > -1; i--) {
            this.cycles[i]--;
            if (this.cycles[i] === 0) {
                const first = this.indices[i];
                for (let j = i; j < this.indices.length - 1; j++)
                    this.indices[j] = this.indices[j + 1];
                this.indices[this.indices.length - 1] = first;
                this.cycles[i] = this.pool.length - i;
            }
            else {
                const j = this.cycles[i];
                const negJ = this.pool.length - j;
                [this.indices[i], this.indices[negJ]] = [this.indices[negJ], this.indices[i]];
                return { done: false, value: this.value };
            }
        }
        return { done: true, value: undefined };
    }
}
export default PermutationsIterator;
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