third-maximum-number.js

/**
 * Third Maximum Number
 *
 * Given a non-empty array of integers, return the third maximum number in this array.
 * If it does not exist, return the maximum number. The time complexity must be in O(n).
 *
 * Example 1:
 *
 * Input: [3, 2, 1]
 *
 * Output: 1
 *
 * Explanation: The third maximum is 1.
 *
 * Example 2:
 *
 * Input: [1, 2]
 *
 * Output: 2
 *
 * Explanation: The third maximum does not exist, so the maximum (2) is returned instead.
 *
 * Example 3:
 *
 * Input: [2, 2, 3, 1]
 *
 * Output: 1
 *
 * Explanation: Note that the third maximum here means the third maximum distinct number.
 * Both numbers with value 2 are both considered as second maximum.
 */

/**
 * @param {number[]} nums
 * @return {number}
 */
const thirdMax = nums => {
  let first = -Infinity;
  let second = -Infinity;
  let third = -Infinity;

  for (let num of nums) {
    if (num === first || num === second || num === third) {
      continue;
    }

    if (num > first) {
      third = second;
      second = first;
      first = num;
    } else if (num > second) {
      third = second;
      second = num;
    } else if (num > third) {
      third = num;
    }
  }

  return third === -Infinity ? first : third;
};

export { thirdMax };