Course Schedule LeetCode solution in JavaScript

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var canFinish = function (numCourses, prerequisites) {
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  const adjList = [];
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  const visit = [];
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  construAdj();
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  for (let i = 0; i < numCourses; i++) {
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    if (!dfs(i)) return false;
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  }
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  return true;
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  function dfs(i) {
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    // base case
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    if (visit[i]) return false;
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    if (visit[i] === false) return true;
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    visit[i] = true;
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    for (const nei of adjList[i] ?? []) {
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      if (!dfs(nei)) return false;
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    }
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    visit[i] = false;
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    return true;
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  }
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  function construAdj() {
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    for (const pre of prerequisites) {
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      if (!adjList[pre[0]]) adjList[pre[0]] = [];
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      adjList[pre[0]].push(pre[1]);
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    }
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  }
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};