JavaScript solution for week 87, part 1.

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+//
+// Challenge
+//
+// You are given an unsorted array of integers @N.
+//
+// Write a script to find the longest consecutive sequence. Print 0 if
+// none sequence found.
+//
+
+//
+// For notes, see the perl solution: ../perl/ch-1.pl
+//
+
+//
+// After reading the input, we put the numbers both in an array
+// (called "array") and an object (called "set").
+// We iterate over the array. If the element has been deleted
+// from the set, we continue with the next element.
+// Else, we construct the longest sequence this element is part
+// off, by starting with the range containing just this element,
+// and extending it on both sides as long as the extension is
+// in the set. We then check whether this improves the best range
+// seen so far (and update the best range), and delete the sequence
+// from the set.
+//
+// When we have processed all numbers, we print the best sequence.
+//
+
+
+//
+// Read STDIN. Split on newlines, then on whitespace, and turn the results
+// into numbers. Since the input will be newline terminated, we have an
+// empty line to filter out.
+//
+let lines = require      ("fs")
+          . readFileSync (0)               // Read all.
+          . toString     ()                // Turn it into a string.
+          . split        ("\n");           // Split on newlines.
+
+
+//
+// Iterate over the lines
+//
+for (let i = 0; i < lines . length - 1; i ++) {
+    //
+    // The line is a set of integers, split on
+    // white space, and store the numbers in a hash.
+    //
+    let array = lines [i] . split (" ") . map (_ => +_);
+    let set   = array . reduce ((acc, val) => {
+        acc [val] = 1;
+        return acc;
+    }, {});
+
+    let best = [0, 0];
+  INNER:
+    for (let i = 0; i < array . length; i ++) {
+        let low  = array [i];
+        if (!set [low]) {
+            continue INNER; // Skip if it's no longer in the set.
+        }
+        let high = low;
+        while (set [low - 1]) {
+            low --;
+        }
+        while (set [high + 1]) {
+            high ++;
+        }
+        if (low < high  &&    // Exclude sequences of length 1
+            high - low > best [1] - best [0]) {
+            best = [low, high];
+        }
+        for (let i = low; i <= high; i ++) {
+            set [i] = 0;
+        }
+    }
+    let str = "";
+    for (let i = best [0]; i <= best [1]; i ++) {
+        str += i;
+        if (i < best [1]) {
+            str += ", ";
+        }
+    }
+    console . log (str);
+}