904. Fruit Into Baskets | zhengxingxing

Method 1

You are visiting a farm that has a single row of fruit trees arranged from left to right. The trees are represented by an integer array fruits where fruits[i] is the type of fruit the ith tree produces.
You want to collect as much fruit as possible. However, the owner has some strict rules that you must follow:
- You only have two baskets, and each basket can only hold a single type of fruit. There is no limit on the amount of fruit each basket can hold.
- Starting from any tree of your choice, you must pick exactly one fruit from every tree (including the start tree) while moving to the right. The picked fruits must fit in one of your baskets.
- Once you reach a tree with fruit that cannot fit in your baskets, you must stop.
Given the integer array fruits, return the maximum number of fruits you can pick.

Example 1

Input: fruits = [1,2,1]
Output: 3
Explanation: We can pick from all 3 trees.

Example 2

Input: fruits = [0,1,2,2]
Output: 3
Explanation: We can pick from trees [1,2,2].
If we had started at the first tree, we would only pick from trees [0,1].

Example 3

Input: fruits = [1,2,3,2,2]
Output: 4
Explanation: We can pick from trees [2,3,2,2].
If we had started at the first tree, we would only pick from trees [1,2].

Method 1

【O(n) time | O(1) space】

package Leetcode.SlideWindow.DynamicSlidingWindow;

import java.util.HashMap;
import java.util.Map;

/**
 * @author zhengxingxing
 * @date 2025/01/15
 */
public class FruitIntoBaskets {
    public static int totalFruit(int[] fruits) {
        int maxFruits = 0; // Maximum number of fruits
        int left = 0;      // Left pointer of sliding window
        Map<Integer, Integer> basket = new HashMap<>(); // Map to track fruit types and their counts

        for (int right = 0; right < fruits.length; right++) {
            // Add current fruit to the basket
            basket.put(fruits[right], basket.getOrDefault(fruits[right], 0) + 1);

            // While we have more than 2 types of fruits in the basket
            while (basket.size() > 2) {
                int leftFruit = fruits[left]; // Get the fruit type at the left pointer
                basket.put(leftFruit, basket.get(leftFruit) - 1); // Decrease the count of that fruit

                // If the count becomes 0, remove this fruit type from the basket
                if (basket.get(leftFruit) == 0) {
                    basket.remove(leftFruit);
                }

                // Move the left pointer to shrink the window
                left++;
            }

            // Update maximum fruits count
            maxFruits = Math.max(maxFruits, right - left + 1);
        }

        return maxFruits; // Return the maximum number of fruits collected
    }

    public static void main(String[] args) {

        // Test Case 1
        int[] test1 = {1, 2, 1};
        System.out.println("Test Case 1 Result: " + totalFruit(test1)); // Expected: 3

        // Test Case 2
        int[] test2 = {0, 1, 2, 2};
        System.out.println("Test Case 2 Result: " + totalFruit(test2)); // Expected: 3

        // Test Case 3
        int[] test3 = {1, 2, 3, 2, 2};
        System.out.println("Test Case 3 Result: " + totalFruit(test3)); // Expected: 4

        // Test Case 4
        int[] test4 = {1, 1, 1, 1};
        System.out.println("Test Case 4 Result: " + totalFruit(test4)); // Expected: 4

        // Test Case 5
        int[] test5 = {};
        System.out.println("Test Case 5 Result: " + totalFruit(test5)); // Expected: 0

        // Test Case 6
        int[] test6 = {5, 2, 5, 2, 5, 2};
        System.out.println("Test Case 6 Result: " + totalFruit(test6)); // Expected: 6
    }
}

Method 1

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