[LeetCode] 904. Fruit Into Baskets

 Problem : https://leetcode.com/problems/fruit-into-baskets/

Use sliding window approach to find the maximum contiguous section contains 2 unique numbers.

Time complexity = O ( N ), N = len(fruits).

Because for each number, it will either be added to the window or removed from the window once.

class Solution {
    public int totalFruit(int[] fruits) {
        int[] counter = new int[fruits.length];
        int uniqNum = 0;

        int result = 0;

        int left = 0;
        for (int right = 0; right < fruits.length; right++) {
            counter[fruits[right]] += 1;
            if (counter[fruits[right]] == 1) {
                uniqNum += 1;
            }

            while (left <= right && uniqNum > 2) {
                counter[fruits[left]] -= 1;
                if (counter[fruits[left]]  == 0) {
                    uniqNum -= 1;
                }
                left += 1;
            }

            result = Math.max(result, right - left + 1);
        }

        return result;
    }
}