add 4-binary

Author: leviding

4-binary/01-arraybuffer-binary-arrays/01-concat/_js.view/solution.js

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+function concat(arrays) {
+  // sum of individual array lengths
+  let totalLength = arrays.reduce((acc, value) => acc + value.length, 0);
+
+  if (!arrays.length) return null;
+
+  let result = new Uint8Array(totalLength);
+
+  // for each array - copy it over result
+  // next array is copied right after the previous one
+  let length = 0;
+  for(let array of arrays) {
+    result.set(array, length);
+    length += array.length;
+  }
+
+  return result;
+}

4-binary/01-arraybuffer-binary-arrays/01-concat/_js.view/source.js

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+function concat(arrays) {
+  // ...your code...
+}
+
+let chunks = [
+  new Uint8Array([0, 1, 2]),
+  new Uint8Array([3, 4, 5]),
+  new Uint8Array([6, 7, 8])
+];
+
+console.log(Array.from(concat(chunks))); // 0, 1, 2, 3, 4, 5, 6, 7, 8
+
+console.log(concat(chunks).constructor.name); // Uint8Array

4-binary/01-arraybuffer-binary-arrays/01-concat/_js.view/test.js

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+describe("concat", function() {
+  let chunks = [
+    new Uint8Array([0, 1, 2]),
+    new Uint8Array([3, 4, 5]),
+    new Uint8Array([6, 7, 8])
+  ];
+
+  it("result has the same array type", function() {
+
+    let result = concat(chunks);
+
+    assert.equal(result.constructor, Uint8Array);
+  });
+
+  it("concatenates arrays", function() {
+
+    let result = concat(chunks);
+
+    assert.deepEqual(result, new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7, 8]));
+
+  });
+
+  it("returns empty array on empty input", function() {
+
+    let result = concat([]);
+
+    assert.equal(result.length, 0);
+
+  });
+
+});

4-binary/01-arraybuffer-binary-arrays/01-concat/solution.md

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+
+# Concatenate typed arrays
+
+Given an array of `Uint8Array`, write a function `concat(arrays)` that returns a concatenation of them into a single array.