112、路径总和

var hasPathSum = function (root, targetSum) {
  if (!root) return false;
  let flag = false;
  const dfs = (root, sum) => {
    if (!root) return;
    if (!root.left && !root.right && sum === targetSum) {
      flag = true;
      return;
    }
    root.left && dfs(root.left, sum + root.left.val);
    root.right && dfs(root.right, sum + root.right.val);
  };
  dfs(root, root.val);
  return flag;
};