in-order.ts

class BinaryNode<T> {
  public constructor(public value: T, public left: BinaryNode<T> = null, public right: BinaryNode<T> = null) {}
}

interface INodeProcessor<T> {
  (value: T): void;
}

interface IBinaryNodeTraversal<T> {
  (node: BinaryNode<T>, processor: INodeProcessor<T>): void;
}

function traverseInOrderRecursive<T>(node: BinaryNode<T>, processor: INodeProcessor<T>): void {
  if (node.left) {
    traverseInOrderRecursive(node.left, processor);
  }
  processor(node.value);
  if (node.right) {
    traverseInOrderRecursive(node.right, processor);
  }
}

function traverseInOrderIterative<T>(node: BinaryNode<T>, processor: INodeProcessor<T>): void {
  class NodeProccessing {
    public constructor(public node: BinaryNode<T>, public leftProcessed: boolean = false, public valueProcessed: boolean = false, public rightProcessed = false) {}
  }

  let stack: NodeProccessing[] = [ new NodeProccessing(node) ];
  while(stack.length !== 0) {
    let frame = stack[stack.length - 1];
    if (frame.node.left && !frame.leftProcessed) {
      frame.leftProcessed = true;
      stack.push(new NodeProccessing(frame.node.left));
      continue;
    }
    if (!frame.valueProcessed) {
      frame.valueProcessed = true;
      processor(frame.node.value);
    }
    if (frame.node.right && !frame.rightProcessed) {
      frame.rightProcessed = true;
      stack.push(new NodeProccessing(frame.node.right));
      continue;
    }
    stack.pop();
  }
}

function binaryTreeToArray<T>(tree: BinaryNode<T>, traversal: IBinaryNodeTraversal<T>): T[] {
  let result: T[] = [];
  let processor: INodeProcessor<T> = v => result.push(v);
  traversal(tree, processor);
  return result;
}

let tree = new BinaryNode(
  5, 
  new BinaryNode(
    3, 
    new BinaryNode(2, new BinaryNode(1), null), 
    new BinaryNode(4, null, null)
  ), 
  new BinaryNode(
    8,
    new BinaryNode(7, new BinaryNode(6), null),
    new BinaryNode(9, null, new BinaryNode(10))
  )
);

console.log(binaryTreeToArray(tree, traverseInOrderRecursive));
console.log(binaryTreeToArray(tree, traverseInOrderIterative));