/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} head
 * @return {boolean}
 */
var hasCycle = function (head) {
  if (head === null) {
    return false;
  }

  let curr = head;
  let next = head.next;

  while (next && next.next) {
    curr = curr.next;
    next = next.next.next;

    if (curr === next) {
      return true;
    }
  }

  return false;
};

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var preorderTraversal = function (root) {
  let result = [];

  traversalHelper(root, result);

  return result;
};

const traversalHelper = (root, result) => {
  if (root === null) {
    return;
  }
  result.push(root.val);
  traversalHelper(root.left, result);
  traversalHelper(root.right, result);
};

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var postorderTraversal = function (root) {
  let result = [];
  traversalHelper(root, result);
  return result;
};

const traversalHelper = (root, result) => {
  if (root === null) {
    return;
  }
  result.unshift(root.val);
  traversalHelper(root.right, result);
  traversalHelper(root.left, result);
};

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} headA
 * @param {ListNode} headB
 * @return {ListNode}
 */
var getIntersectionNode = function (headA, headB) {
  if (!headA || !headB) {
    return null;
  }

  let nodeA = headA;
  let nodeB = headB;

  while (nodeA !== nodeB) {
    nodeA = nodeA.next;
    nodeB = nodeB.next;

    console.log(nodeA, nodeB);

    if (nodeA === nodeB) {
      return nodeA;
    }

    if (!nodeA) {
      nodeA = headB;
    }
    if (!nodeB) {
      nodeB = headA;
    }
  }

  return nodeA;
};

/**
 * @param {number} columnNumber
 * @return {string}
 */
var convertToTitle = function (columnNumber) {
  // String.fromCharCode(65) === "A"
  // 한 자릿수일 경우
  if (columnNumber - 1 < 26) {
    return String.fromCharCode(65 + ((columnNumber - 1) % 26));
  }

  // 두 자릿수 이상일 경우
  let result = '';
  while (columnNumber > 0) {
    const remainder = (columnNumber - 1) % 26;
    const remainderCharCode = String.fromCharCode(65 + remainder);
    result = remainderCharCode + result;
    columnNumber = parseInt((columnNumber - 1) / 26);
  }
  return result;
};

/**
 * @param {number[]} nums
 * @return {number}
 */
var majorityElement = function (nums) {
  const element = {};

  for (const num of nums) {
    if (element[num]) {
      element[num]++;
    } else {
      element[num] = 1;
    }
  }

  let max = 0;
  let targetNum = '';

  for (let e in element) {
    if (element[e] > max) {
      max = element[e];
      targetNum = e;
    }
  }

  return Number(targetNum);
};

/**
 * @param {string} columnTitle
 * @return {number}
 */
var titleToNumber = function (columnTitle) {
  if (columnTitle.length === 1) {
    return (columnTitle.charCodeAt(0) % 65) + 1;
  }

  let result = 0;

  for (let i = columnTitle.length - 1; i >= 0; i--) {
    const strCode = (columnTitle[i].charCodeAt(0) % 65) + 1;
    if (i === columnTitle.length - 1) {
      result += strCode;
    } else {
      result += strCode * 26 ** (columnTitle.length - i - 1);
    }
  }
  return result;
};

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function (s) {
  if (s.length % 2 !== 0) {
    return false;
  }

  const stack = [];
  const brackets = {
    '(': ')',
    '{': '}',
    '[': ']',
  };

  for (let i = 0; i < s.length; i++) {
    if (Object.keys(brackets).includes(s[i])) {
      stack.push(s[i]);
    } else {
      if (brackets[stack[stack.length - 1]] === s[i]) {
        stack.pop();
      } else {
        return false;
      }
    }
  }
  return stack.length === 0;
};

/**
 * @param {number} n
 * @return {boolean}
 */
var isHappy = function (n) {
  let set = new Set();

  while (!set.has(n)) {
    set.add(n);
    let s = n.toString();
    n = 0;
    for (let i = 0; i < s.length; ++i) {
      n += squares[s[i]];
    }
    if (n === 1) return true;
  }

  return false;
};

const squares = {
  0: 0,
  1: 1,
  2: 4,
  3: 9,
  4: 16,
  5: 25,
  6: 36,
  7: 49,
  8: 64,
  9: 81,
};

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isIsomorphic = function (s, t) {
  if (s.length !== t.length) {
    return false;
  }

  if (s === t) {
    return true;
  }

  for (let i = 0; i < s.length; i++) {
    if (s.indexOf(s[i]) !== t.indexOf(t[i])) {
      return false;
    }
  }
  return true;
};