Exercise 34,35,36

Author: AvraamMavridis

README.md

@@ -50,6 +50,9 @@
 - <a href="https://github.com/AvraamMavridis/FE-questions-answers/blob/master/exercises/exercise31.md">31. Move all instances of a value in an array at the end of the array</a>
 - <a href="https://github.com/AvraamMavridis/FE-questions-answers/blob/master/exercises/exercise32.md">32. Sort a linked list</a>
 - <a href="https://github.com/AvraamMavridis/FE-questions-answers/blob/master/exercises/exercise33.md">33. Circle in linked list</a>
+- <a href="https://github.com/AvraamMavridis/FE-questions-answers/blob/master/exercises/exercise34.md">34. Verify that a binary tree is a binary search tree.</a>
+- <a href="https://github.com/AvraamMavridis/FE-questions-answers/blob/master/exercises/exercise35.md">35. Implement a Stack using two Queues..</a>
+- <a href="https://github.com/AvraamMavridis/FE-questions-answers/blob/master/exercises/exercise36.md">36. Fibonacci recursive, recursive with memoization, and iterative..</a>
 
 <a href="https://github.com/AvraamMavridis/FE-questions-answers/blob/master/exerciseUtils.md">Various Utils helpful to generate test data</a>
 

exercises/exercise35.md

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+## Exercise
+
+Implement a Stack using two Queues.
+
+## Solution
+
+```ts
+class Queue {
+  _queue: Array<number>
+
+  constructor(){
+    this._queue = [];
+  }
+
+  enqueue(value: number){
+    this._queue.push(value)
+  }
+
+  dequeue(){
+    return this._queue.shift();
+  }
+
+  getSize(){
+    return this._queue.length;
+  }
+}
+
+
+class Stack {
+  qu1: Queue;
+  qu2: Queue;
+
+  constructor() {
+    this.qu1 = new Queue();
+    this.qu2 = new Queue();
+  }
+
+  push(value: number){
+    this.qu1.enqueue(value);
+  }
+
+  pop(){
+    let value = undefined;
+    while(this.qu1.getSize() > 1){
+      this.qu2.enqueue(this.qu1.dequeue())
+    }
+
+    value = this.qu1.dequeue();
+
+    while(this.qu2.getSize()){
+      this.qu1.enqueue(this.qu2.dequeue())
+    }
+
+    return value;
+  }
+}
+
+const s = new Stack();
+
+s.push(10);
+s.push(30);
+s.push(50);
+console.assert(s.pop() === 50, 'Wrong implementation');
+
+s.push(40);
+s.push(90);
+console.log(s.pop() === 90, 'Wrong implementation');
+```

exercises/exercise36.md

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+## Exercise
+
+Fibonacci recursive, recursive with memoization, and iterative
+
+## Solution
+
+```ts
+/**
+ * Recursive
+ * @param {number} n
+ */
+const fbn = function(n: number) {
+  if (n === 0) return 0;
+  if (n === 1) return 1;
+  return fbn(n - 1) + fbn(n - 2);
+};
+
+/**
+ * Recursive with memoization
+ *
+ * @param {number} n
+ * @returns {number}
+ */
+const fbnMemo = function(n: number) {
+  const memo = {};
+
+  const fbnM = function(n) {
+    if (n === 0) return 0;
+    if (n === 1) return 1;
+    if (memo[`${n}`]) return memo[`${n}`];
+
+    memo[`${n}`] = fbnM(n - 1) + fbnM(n - 2);
+    return memo[`${n}`];
+  };
+
+  return fbnM(n);
+};
+
+/**
+ * Recursive Iterative
+ *
+ * @param {number} n
+ * @returns {number}
+ */
+const fbnIt = function(n: number) {
+  let vals = [0, 1];
+  if (n === 0) return vals[0];
+  if (n === 1) return vals[1];
+
+  for (let i = 0; i < n - 1; i++) {
+    [vals[0], vals[1]] = [vals[1], vals[0] + vals[1]];
+  }
+
+  return vals[1];
+};
+
+console.assert(fbn(10) === fbnM(10) === fbnIt(10), "Wrong Implementation");
+```