17.树的子结构

/* function TreeNode(x) {
  this.val = x;
  this.left = null;
  this.right = null;
} */
function HasSubtree(root1, root2) {
  // write code here
  if (root1 === null || root2 === null) {
    return false;
  }
  let result = false;
  if (root1.val === root2.val) {
    result = helper(root1, root2);
  }
  if (!result) {
    result = helper(root1.left, root2);
  }
  if (!result) {
    result = helper(root1.right, root2);
  }
  return result;
}

function helper(r1, r2) {
  if (r2 === null) return true;
  if (r1 === null) return false;
  if (r1.val != r2.val) return false;
  return helper(r1.left, r2.left) && helper(r1.right, r2.right);
}