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Commit 72058e4

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feat(book/graph): add schedule exercise and solution
1 parent 802e9d3 commit 72058e4

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2 files changed

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// tag::description[]
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function canFinish(n, prerequisites) {
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// end::description[]
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// tag::placeholder[]
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// write your code here...
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// end::placeholder[]
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// tag::solution[]
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const graph = new Map(Array(n).fill().map((v, i) => ([i, []])));
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prerequisites.forEach(([u, v]) => graph.get(v).push(u));
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const seen = [];
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const hasCycle = (node) => {
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if (seen[node] === 1) return true; // if visiting, it's a cycle!
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if (seen[node] === 2) return false; // if visited, skip it.
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seen[node] = 1; // mark as visiting.
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for (const adj of graph.get(node)) if (hasCycle(adj)) return true;
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seen[node] = 2; // mark as visited.
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return false;
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};
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for (let i = 0; i < n; i++) if (hasCycle(i)) return false;
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return true;
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// end::solution[]
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// tag::description[]
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}
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// end::description[]
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module.exports = { canFinish };
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const { canFinish } = require('./course-schedule');
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// const { } = require('../../src/index');
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[canFinish].forEach((fn) => {
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describe(`TOPIC: ${fn.name}`, () => {
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it('should work with null/empty', () => {
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const actual = [];
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const expected = true;
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expect(fn(0, actual)).toEqual(expected);
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});
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it('should work basic case', () => {
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const actual = [[1, 0]];
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const courses = 2;
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const expected = true;
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expect(fn(courses, actual)).toEqual(expected);
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});
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it('should detect cycle', () => {
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const actual = [[0, 1], [1, 0]];
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const courses = 2;
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const expected = false;
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expect(fn(courses, actual)).toEqual(expected);
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});
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it('multiple links to a node without cycle', () => {
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const actual = [[2, 1], [1, 0], [2, 0]];
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const courses = 3;
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const expected = true;
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expect(fn(courses, actual)).toEqual(expected);
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});
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it('multiple links to a node without cycle (different order)', () => {
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const actual = [[2, 0], [1, 0], [2, 1]];
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const courses = 3;
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const expected = true;
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expect(fn(courses, actual)).toEqual(expected);
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});
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it('indirect cycle', () => {
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const actual = [[1, 0], [2, 1], [0, 2]];
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const courses = 3;
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const expected = false;
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expect(fn(courses, actual)).toEqual(expected);
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});
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it('indirect cycle with nodes without indegrees', () => {
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const actual = [[1, 0], [2, 1], [3, 2], [1, 3]];
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const courses = 4;
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const expected = false;
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expect(fn(courses, actual)).toEqual(expected);
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});
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});
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});

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