Data update

Task/Stream-merge/JavaScript/stream-merge.js

@@ -0,0 +1,89 @@
+// ------------------------------------------------------------
+// Helper that prints a number followed by a space (like C++ `display`)
+function display(num) {
+  process.stdout.write(num + ' ');
+}
+
+// ------------------------------------------------------------
+// merge2 – merge two sorted collections and call `action` for each
+// element in sorted order.
+function merge2(c1, c2, action) {
+  let i1 = 0;                 // index into c1
+  let i2 = 0;                 // index into c2
+
+  while (i1 < c1.length && i2 < c2.length) {
+    if (c1[i1] <= c2[i2]) {
+      action(c1[i1++]);
+    } else {
+      action(c2[i2++]);
+    }
+  }
+
+  // copy the rest of c1 (if any)
+  while (i1 < c1.length) {
+    action(c1[i1++]);
+  }
+
+  // copy the rest of c2 (if any)
+  while (i2 < c2.length) {
+    action(c2[i2++]);
+  }
+}
+
+// ------------------------------------------------------------
+// mergeN – merge **any number** of sorted collections.
+// `all` is an iterable (e.g. an array) that contains the
+// collections to be merged.  `action` is called for each value
+// in global sorted order.
+function mergeN(action, all) {
+  // Create a list of “ranges”: each entry keeps the source array
+  // and the current index inside that array.
+  const ranges = Array.from(all, col => ({
+    arr: col,
+    pos: 0,                // points to the next element to read
+    end: col.length
+  }));
+
+  let done = false;
+  while (!done) {
+    done = true;
+    let least = null;      // reference to the range that currently has the smallest element
+
+    // Scan every range looking for the smallest next element.
+    for (const r of ranges) {
+      // skip exhausted ranges
+      if (r.pos >= r.end) continue;
+
+      if (least === null || r.arr[r.pos] < least.arr[least.pos]) {
+        least = r;
+      }
+    }
+
+    // If we found a non‑empty range, emit its element and advance it.
+    if (least !== null) {
+      done = false;
+      action(least.arr[least.pos]);
+      ++least.pos;
+    }
+  }
+}
+
+// ------------------------------------------------------------
+// Demo – the same tests that the C++ `main` performed
+(function main() {
+  const v1 = [0, 3, 6];
+  const v2 = [1, 4, 7];
+  const v3 = [2, 5, 8];
+
+  // merge2(v2, v1, display);
+  merge2(v2, v1, display);
+  console.log();                     // newline
+
+  // mergeN(display, { v1 });
+  mergeN(display, [v1]);
+  console.log();
+
+  // mergeN(display, { v3, v2, v1 });
+  mergeN(display, [v3, v2, v1]);
+  console.log();
+})();