const levenshteinDistance = (s, t) => {
  if (!s.length) return t.length;
  if (!t.length) return s.length;
  const arr = [];
  for (let i = 0; i <= t.length; i++) {
    arr[i] = [i];
    for (let j = 1; j <= s.length; j++) {
      arr[i][j] =
        i === 0
          ? j
          : Math.min(
              arr[i - 1][j] + 1,
              arr[i][j - 1] + 1,
              arr[i - 1][j - 1] + (s[j - 1] === t[i - 1] ? 0 : 1)
            );
    }
  }
  return arr[t.length][s.length];
};

levenshteinDistance('duck', 'dark'); // 2

var invertTree = function(root) {
    const reverseNode = node => {
        if (node == null) {
            return null
        }
        reverseNode(node.left);
        reverseNode(node.right);
        let holdLeft = node.left;
        node.left = node.right;
        node.right = holdLeft;
        return node;
    }

    return reverseNode(root);
};

const copyToClipboard = str => {
  const el = document.createElement('textarea');
  el.value = str;
  el.setAttribute('readonly', '');
  el.style.position = 'absolute';
  el.style.left = '-9999px';
  document.body.appendChild(el);
  const selected =
    document.getSelection().rangeCount > 0
      ? document.getSelection().getRangeAt(0)
      : false;
  el.select();
  document.execCommand('copy');
  document.body.removeChild(el);
  if (selected) {
    document.getSelection().removeAllRanges();
    document.getSelection().addRange(selected);
  }
};

copyToClipboard('Lorem ipsum'); // 'Lorem ipsum' copied to clipboard.

// Or
const randomColor = () => `#${(~~(Math.random()*(1<<24))).toString(16)}`;
console.log(randomColor);

function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

function App() {
  return (
    <div>
      <Welcome name="Sara" />
      <Welcome name="Cahal" />
      <Welcome name="Edite" />
    </div>
  );
}

ReactDOM.render(
  <App />,
  document.getElementById('root')
);

const countSubstrings = (str, searchValue) => {
  let count = 0,
    i = 0;
  while (true) {
    const r = str.indexOf(searchValue, i);
    if (r !== -1) [count, i] = [count + 1, r + 1];
    else return count;
  }
};

countSubstrings('tiktok tok tok tik tok tik', 'tik'); // 3
countSubstrings('tutut tut tut', 'tut'); // 4