code from chapter 4 in javascript

04_quicksort/01_loop_sum.js

@@ -0,0 +1,11 @@
+'use strict';
+
+function sum(arr) {
+  let total = 0;
+  for (let x = 0; x < arr.length; x++) {
+    total += arr[x];
+  }
+  return total;
+}
+
+console.log(sum([1, 2, 3, 4])) // 10

04_quicksort/02_recursive_sum.js

@@ -0,0 +1,10 @@
+'use strict';
+
+function sum(list) {
+  if (list.length === 0) {
+    return 0;
+  }
+  return list[0] + sum(list.slice(1));
+}
+
+console.log(sum([1, 2, 3, 4])) // 10

04_quicksort/03_recursive_count.js

@@ -0,0 +1,10 @@
+'use strict';
+
+function count(list) {
+  if (list.length === 0) {
+    return 0;
+  }
+  return 1 + count(list.slice(1));
+}
+
+console.log(count([0, 1, 2, 3, 4, 5])); // 6

04_quicksort/04_recursive_max.js

@@ -0,0 +1,11 @@
+'use strict';
+
+function max(list) {
+  if (list.length === 2) {
+    return list[0] > list[1] ? list[0] : list[1];
+  }
+  let sub_max = max(list.slice(1));
+  return list[0] > sub_max ? list[0] : sub_max;
+}
+
+console.log(max([1, 5, 10, 25, 16, 1])); // 25

04_quicksort/05_quicksort.js

@@ -0,0 +1,18 @@
+'use strict';
+
+function quicksort(array) {
+  if (array.length < 2) {
+    // base case, arrays with 0 or 1 element are already "sorted"
+    return array;
+  } else {
+   // recursive case
+   let pivot = array[0];
+   // sub-array of all the elements less than the pivot
+   let less = array.slice(1).filter(function(el) { return el <= pivot; });
+   // sub-array of all the elements greater than the pivot
+   let greater = array.slice(1).filter(function(el) { return el > pivot; });
+   return quicksort(less).concat([pivot], quicksort(greater));
+  }
+}
+
+console.log(quicksort([10, 5, 2, 3])); // [2, 3, 5, 10]