The challenge
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.
The solution
I have seen many possible resolutions to this problem, but my favourite has to be the following:
class Solution {
// input a primitive array of ints and return an int
public int thirdMax(int[] nums) {
// set variables for our 3 max'es
Integer max1 = null;
Integer max2 = null;
Integer max3 = null;
// loop through the input array
for (Integer n : nums) {
// if already set, then skip this loop iteration
if (n.equals(max1) || n.equals(max2) || n.equals(max3)) continue;
// if 1
if (max1 == null || n > max1) {
max3 = max2;
max2 = max1;
max1 = n;
// if 2
} else if (max2 == null || n > max2) {
max3 = max2;
max2 = n;
// if 3
} else if (max3 == null || n > max3) {
max3 = n;
}
}
// return max3, unless null
return max3 == null ? max1 : max3;
}
}