Add missing solutions for algorithm challenges (#38858)

curriculum/challenges/english/10-coding-interview-prep/algorithms/implement-merge-sort.english.md

@@ -79,7 +79,37 @@ function isSorted(arr) {
 <section id='solution'>
 
 ```js
-// solution required
+function mergeSort(array) {
+  if (array.length === 1) {
+    return array;
+  } else {
+    const splitIndex = Math.floor(array.length / 2);
+    return merge(
+      mergeSort(array.slice(0, splitIndex)),
+      mergeSort(array.slice(splitIndex))
+    );
+  }
+
+  // Merge two sorted arrays
+  function merge(array1, array2) {
+    let merged = [];
+    while (array1.length && array2.length) {
+      if (array1[0] < array2[0]) {
+        merged.push(array1.shift());
+      } else if (array1[0] > array2[0]) {
+        merged.push(array2.shift());
+      } else {
+        merged.push(array1.shift(), array2.shift());
+      }
+    }
+
+    // After looping ends, one array is empty, and other array contains only
+    // values greater than all values in `merged`
+    return [...merged, ...array1, ...array2];
+  }
+}
+
+mergeSort([1, 4, 2, 8, 345, 123, 43, 32, 5643, 63, 123, 43, 2, 55, 1, 234, 92]);
 ```
 
 </section>

curriculum/challenges/english/10-coding-interview-prep/algorithms/implement-quick-sort.english.md

@@ -75,7 +75,32 @@ function isSorted(arr) {
 <section id='solution'>
 
 ```js
-// solution required
+function quickSort(array) {
+  if (array.length === 0) {
+    return [];
+  } else {
+    const pivotValue = array[0];
+
+    // Sort elements into three piles
+    let lesser = [];
+    let equal = [];
+    let greater = [];
+    for (let e of array) {
+      if (e < pivotValue) {
+        lesser.push(e);
+      } else if (e > pivotValue) {
+        greater.push(e);
+      } else {
+        equal.push(e);
+      }
+    }
+
+    return [...quickSort(lesser), ...equal, ...quickSort(greater)];
+  }
+}
+
+// test array:
+// [1, 4, 2, 8, 345, 123, 43, 32, 5643, 63, 123, 43, 2, 55, 1, 234, 92]
 ```
 
 </section>