Add code for chapter 3 and 4 in ts (#103)

03_recursion/ts/01_countdown.ts

@@ -0,0 +1,13 @@
+function countdown(i: number): null {
+    console.log(i);
+
+    if (i <= 0) {
+        return null;
+    }
+
+    countdown(i-1);
+
+    return null;
+}
+
+console.log(countdown(5));

03_recursion/ts/02_greet.ts

@@ -0,0 +1,16 @@
+function greet2(name: string): void {
+    console.log('how are you, ' + name + '?');
+}
+
+function bye(): void {
+    console.log('ok bye!');
+}
+
+function greet(name: string): void {
+    console.log('hello, ' + name + '!');
+    greet2(name);
+    console.log('getting ready to say bye...');
+    bye();
+}
+
+greet('adit');

03_recursion/ts/03_factorial.ts

@@ -0,0 +1,9 @@
+function fact(x: number): number {
+    if (x === 1) {
+        return x;
+    }
+
+    return x * fact(x - 1);
+}
+
+console.log(fact(5));

04_quicksort/ts/01_loop_sum.ts

@@ -0,0 +1,10 @@
+function sum(arr: number[]): number {
+    let total = 0;
+    arr.forEach(number => {
+        total += number;
+    });
+
+    return total;
+}
+
+console.log(sum([1, 2, 3, 4]));

04_quicksort/ts/02_recursive_sum.ts

@@ -0,0 +1,9 @@
+function sum(arr: number[]): number {
+    if (arr.length === 1) {
+        return arr[0];
+    }
+
+    return arr[0] + sum(arr.slice(1));
+}
+
+console.log(sum([1, 2, 3, 4]));

04_quicksort/ts/03_recursive_count.ts

@@ -0,0 +1,9 @@
+function count<T>(list: T[]): number {
+    if (list.length === 1) {
+        return 1;
+    }
+
+    return 1 + count(list.slice(1));
+}
+
+console.log(count([1, 2, 3]));

04_quicksort/ts/04_recursive_max.ts

@@ -0,0 +1,15 @@
+function max(arr: number[]): number | null {
+    if (arr.length === 0) {
+        return null;
+    }
+
+    if (arr.length === 1) {
+        return arr[0];
+    }
+
+    const subMax = max(arr.slice(1));
+
+    return arr[0] > subMax ? arr[0] : subMax;
+};
+
+console.log(max([1, 2, 4, 3]));

04_quicksort/ts/05_quicksort.ts

@@ -0,0 +1,13 @@
+function quicksort(arr: number[]): number[] {
+    if (arr.length < 2) {
+        return arr;
+    }
+
+    const pivot = arr[0];
+    const less = arr.slice(1).filter(el => el <= pivot);
+    const greater = arr.slice(1).filter(el => el > pivot);
+
+    return quicksort(less).concat(pivot, quicksort(greater));
+}
+
+console.log(quicksort([10, 5, 2, 3]));