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.

Solution

public class Solution {
 public int thirdMax(int[] nums) {
        if (nums == null || nums.length == 0) return -1;

        int one = Integer.MIN_VALUE;
        int two = Integer.MIN_VALUE;
        int three = Integer.MIN_VALUE;

        for (int i = 0; i < nums.length; i++) {
            if (nums[i] > one) {
                one = nums[i];
            }
        }

        for(int i : nums) {
            if (i>two && i < one) {
                two = i;
            }
        }

        boolean flag = false;
        for(int i : nums) {
            if (i>= three && i < two) {
                three = i;
                flag = true;
            }
        }

        if (flag) {
            return three;
        } else {
            return one;
        }

    }
}