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  1. PO
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    <p>My other answer explains why your sort does not work stable. This one will solve your actual problem :-)</p> <p>You can't use a <code>sort</code> for this type of problem, where you want to construct a list of nodes from a (unordered) set of edges. Sorting an array is only applicable if you can <em>compare</em> two of the elements without additional data. Say you have only the two connections <code>Tokio - Moscow</code> and <code>Rome - Oslo</code>, you don't know which of them comes first (without contacting your plan, but you don't have that yet). In contrast, when comparing numbers you can easily and always tell that 5 is bigger than 3 (by computing the difference).</p> <p>Instead, we need to do something like <a href="https://stackoverflow.com/a/12048098/1048572">this</a> or <a href="https://stackoverflow.com/a/14252219/1048572">this</a> - build a structure where we can easily access a station by name and insert connections directly when we encounter them during looping them, so that in the end we have a list of connections by station:</p> <pre><code>var map = {}; for (var i=0; i&lt;arr.length; i++) { var con = arr[i]; map[con.from] = con; } </code></pre> <p>So that we can now construct your route as some kind of linked list:</p> <pre><code>for (var from in map) { var connTo = map[from].to; if (connTo in map) map[from].next = map[connTo]; } </code></pre> <p>And find the start station by deleting all destinations from the map:</p> <pre><code>for (var from in map) for (var next = map[from]; next; next = next.next) delete map[next.to]; for (from in map) // there's only one key left var start = from; // "Helsinki" </code></pre> <p>Let's construct the route as an array of station names:</p> <pre><code>var route = [start], conn = map[start]; while (conn) { route.push(conn.to) conn = conn.next; // maybe delete conn.next as we don't need it any more } // route: // ["Helsinki", "Tokio", "Moscow", "Rome", "Oslo", "Paris", "New-York"] </code></pre> <p>or the result which you want, the list of connections:</p> <pre><code>var arr = []; for (var conn = map[start]; conn; conn = conn.next) arr.push(conn); </code></pre> <hr> <p>Having that plan, we even could now construct a compare-function to sort the original array:</p> <pre><code>arr.sort(function(a, b) { // compare the positions of the departure stations in the route return route.indexOf(a.from) - route.indexOf(b.from); }); </code></pre>
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    1. COit's genious. really. thank you for this wonderful answer, your saving my brain in safety)
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    2. COwell i found i don't quite understand this fragment: `for (var from in map) for (var next = map[from]; next; next = next.next) delete map[next.to]; for (from in map) var start = from;` i want to understand how it works but confused at this wild cycle `for (var next = map[from]; next; next = next.next)`
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    3. COmay be i can find start place without deleting but with `if` which will find that name of the start place is not one of the name of the arrival place?
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