904. Fruit Into Baskets #

Problem #

In a row of trees, the i-th tree produces fruit with type tree[i].

You start at any tree of your choice, then repeatedly perform the following steps:

1. Add one piece of fruit from this tree to your baskets. If you cannot, stop.
2. Move to the next tree to the right of the current tree. If there is no tree to the right, stop.

Note that you do not have any choice after the initial choice of starting tree: you must perform step 1, then step 2, then back to step 1, then step 2, and so on until you stop.

You have two baskets, and each basket can carry any quantity of fruit, but you want each basket to only carry one type of fruit each.

What is the total amount of fruit you can collect with this procedure?

Example 1:

Input: [1,2,1]
Output: 3
Explanation: We can collect [1,2,1].

Example 2:

Input: [0,1,2,2]
Output: 3
Explanation: We can collect [1,2,2].
If we started at the first tree, we would only collect [0, 1].

Example 3:

Input: [1,2,3,2,2]
Output: 4
Explanation: We can collect [2,3,2,2].
If we started at the first tree, we would only collect [1, 2].

Example 4:

Input: [3,3,3,1,2,1,1,2,3,3,4]
Output: 5
Explanation: We can collect [1,2,1,1,2].
If we started at the first tree or the eighth tree, we would only collect 4 fruits.

Note:

• 1 <= tree.length <= 40000
• 0 <= tree[i] < tree.length

Problem Summary #

This problem tests the sliding window technique.

Given an array, the numbers in the array represent the types of fruit on each fruit tree; 1 represents fruit type 1, and different numbers represent different fruits. Now there are 2 baskets, and each basket can only hold one type of fruit, which means only 2 different numbers can be chosen. Fruit can only be picked from left to right, stopping when there is no fruit to pick on the right. Ask for the length of the longest contiguous interval of fruit that can be picked.

Solution Approach #

To simplify the problem, given a sequence of numbers, find the maximum length of an interval containing 2 different numbers. This interval can only contain these 2 different numbers, and they can repeat, but it cannot contain any other numbers.

Just handle it using the typical sliding window approach.

Code #

package leetcode

func totalFruit(tree []int) int {
	if len(tree) == 0 {
		return 0
	}
	left, right, counter, res, freq := 0, 0, 1, 1, map[int]int{}
	freq[tree[0]]++
	for left < len(tree) {
		if right+1 < len(tree) && ((counter > 0 && tree[right+1] != tree[left]) || (tree[right+1] == tree[left] || freq[tree[right+1]] > 0)) {
			if counter > 0 && tree[right+1] != tree[left] {
				counter--
			}
			right++
			freq[tree[right]]++
		} else {
			if counter == 0 || (counter > 0 && right == len(tree)-1) {
				res = max(res, right-left+1)
			}
			freq[tree[left]]--
			if freq[tree[left]] == 0 {
				counter++
			}
			left++
		}
	}
	return res
}