Create an algorithm to decide if T2 is a subtree of T1.

containTrees

function containTrees(tree1, tree2){
  if (tree2 === null){
      return true;
  }
  
  return subTree(tree1, tree2);
}

function subTree(tree1, tree2){
  if (tree1 === null){
      return false;
  }
  
  if (tree1.val === tree2.val){
      return matchTree(tree1, tree2);
  }
  
  return subTree(tree1.left, tree2) || subTree(tree1.right, tree2);
}

function matchTree(tree1, tree2){
    if ((tree1 === null) && (tree2 === null)) return true;
    
    if (tree1 === null || tree2 === null) {
        return false;
    }
    
    if (tree1.val !== tree2.val){
        return false;
    }
    
    return (matchTree(tree1.left, tree2.left) && matchTree(tree1.right, tree2.right))
}

// var large = {val:10, left:null, right:null};
// var a = {val:1, left:null, right:null};
// var b = {val:2, left:null, right:null};
// var c = {val:3, left:null, right:null};
// var d = {val:4, left:null, right:null};
// large.left = a;
// a.left = b;
// a.right = c;
// b.left = d;

// var small = {val:1, left:null, right:null};
// var b = {val:2, left:null, right:null};
// var c = {val:3, left:null, right:null};
// var d = {val:4, left:null, right:null};
// small.left = b;
// small.right = c;
// b.left = d;

// console.log(containTrees(large, small));