Minimum Time to Collect All Apples in a Tree LeetCode solution in JavaScript

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var cnvrtAdjLst = (mat) => {
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  //converts the list of edges to adjacency list
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  let map = new Map();
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  for (let i = 0; i < mat.length; i++) {
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    let [p, c] = mat[i];
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    if (map[p] === undefined) map[p] = [c];
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    else map[p].push(c);
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    if (map[c] === undefined) map[c] = [p];
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    else map[c].push(p);
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  }
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  return map;
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};
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var minTime = function (n, edges, hasApple) {
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  let adjList = cnvrtAdjLst(edges); //convert to adjacency list for undirected graph
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  let visited = new Set(); // visited set for checking trivial loop
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  let dfsForApples = (src, len) => {
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    visited.add(src); // add root to visited set, as we start exploring the subtree
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    let lengthFromNow = 0; //total length of path visited by each child, 0 if no child has apple
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    for (let i in adjList[src]) {
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      if (!visited.has(adjList[src][i])) {
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        lengthFromNow += dfsForApples(adjList[src][i], len + 1); // add child path length to total length
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      }
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    }
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    if (lengthFromNow > 0) {
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      //if there is an apple present in the subtree
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      return lengthFromNow + 2;
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    } else if (hasApple[src]) {
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      //if there is no apple in subtree but apple is present on the root node
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      return 2;
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    } else {
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      // if no apple is present in subtree
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      return 0;
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    }
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  };
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  visited.add(0);
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  let res = dfsForApples(0, 0);
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  return res ? res - 2 : 0; //check if the root node itself has an apple or no apple is present
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};