Algorithms: Implement Merge Sort

Algorithms/mergeSort.js

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+// https://www.freecodecamp.org/learn/coding-interview-prep/algorithms/implement-merge-sort
+
+function mergeSort(array) {
+  // Only change code below this line
+  let merges = Math.floor(array.length / 2);
+  let mergeSize = 1;
+  let stop = false;
+  while (!stop) {
+    stop = merges ? false : true;
+    const array2 = [];
+    for (let i = 0; i <= merges; i++) {
+      const leftArrayStart = i * mergeSize * 2;
+      const rightArrayStart = leftArrayStart + mergeSize;
+      const leftArrayEnd = Math.min(rightArrayStart, array.length);
+      const rightArrayEnd = Math.min(rightArrayStart + mergeSize, array.length);
+      let leftI = leftArrayStart; // left array pointer
+      let rightI = rightArrayStart; // right array pointer
+      while (leftI < leftArrayEnd && rightI < rightArrayEnd) {
+        if (array[leftI] <= array[rightI]) {
+          array2.push(array[leftI++]);
+        } else {
+          array2.push(array[rightI++]);
+        }
+      }
+      while (leftI < leftArrayEnd) {
+        array2.push(array[leftI++]);
+      }
+      while (rightI < rightArrayEnd) {
+        array2.push(array[rightI++]);
+      }
+    }
+
+    array = array2;
+    mergeSize *= 2;
+    merges = Math.floor(merges / 2);
+  }
+  return array;
+  // Only change code above this line
+}
+
+console.log(mergeSort([4, 2, 1, 6, 5, 3, 0]));
+console.log(
+  mergeSort([
+    1, 4, 2, 8, 345, 123, 43, 32, 5643, 63, 123, 43, 2, 55, 1, 234, 92,
+  ])
+);