class Node {
  constructor(value, left = null, right = null) {
    this.value = value;
    this.left = left;
    this.right = right;
  }
}

//     40
//    /  \
//  20    60
//  / \   / \
// 10 30  50 70
// Result: 4

function getLeafCountOfBinaryTree(node) {
  if(node === null) return 0;
  if(node.left === null && node.right === null) return 1;
  return getLeafCountOfBinaryTree(node.left) + getLeafCountOfBinaryTree(node.right);
}


let rootNode =new Node(40);
let node20=new Node(20);
let node10=new Node(10);
let node30=new Node(30);
let node60=new Node(60);
let node50=new Node(50);
let node70=new Node(70);

rootNode.left=node20;
rootNode.right=node60;

node20.left=node10;
node20.right=node30;

node60.left=node50;
node60.right=node70;

console.log(getLeafCountOfBinaryTree(rootNode));