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].
Constraints:
1 <= fruits.length <= 1050 <= fruits[i] < fruits.length
We use a hash table
We traverse the fruits array, add the current fruit
After the traversal ends, we can get the final answer.
1 2 3 2 2 1 4
^ ^
j i
1 2 3 2 2 1 4
^ ^
j i
1 2 3 2 2 1 4
^ ^
j i
The time complexity is fruits array.
class Solution:
def totalFruit(self, fruits: List[int]) -> int:
cnt = Counter()
ans = j = 0
for i, x in enumerate(fruits):
cnt[x] += 1
while len(cnt) > 2:
y = fruits[j]
cnt[y] -= 1
if cnt[y] == 0:
cnt.pop(y)
j += 1
ans = max(ans, i - j + 1)
return ansclass Solution {
public int totalFruit(int[] fruits) {
Map<Integer, Integer> cnt = new HashMap<>();
int ans = 0;
for (int i = 0, j = 0; i < fruits.length; ++i) {
int x = fruits[i];
cnt.merge(x, 1, Integer::sum);
while (cnt.size() > 2) {
int y = fruits[j++];
if (cnt.merge(y, -1, Integer::sum) == 0) {
cnt.remove(y);
}
}
ans = Math.max(ans, i - j + 1);
}
return ans;
}
}class Solution {
public:
int totalFruit(vector<int>& fruits) {
unordered_map<int, int> cnt;
int ans = 0;
for (int i = 0, j = 0; i < fruits.size(); ++i) {
int x = fruits[i];
++cnt[x];
while (cnt.size() > 2) {
int y = fruits[j++];
if (--cnt[y] == 0) {
cnt.erase(y);
}
}
ans = max(ans, i - j + 1);
}
return ans;
}
};func totalFruit(fruits []int) int {
cnt := map[int]int{}
ans, j := 0, 0
for i, x := range fruits {
cnt[x]++
for ; len(cnt) > 2; j++ {
y := fruits[j]
cnt[y]--
if cnt[y] == 0 {
delete(cnt, y)
}
}
ans = max(ans, i-j+1)
}
return ans
}function totalFruit(fruits: number[]): number {
const n = fruits.length;
const cnt: Map<number, number> = new Map();
let ans = 0;
for (let i = 0, j = 0; i < n; ++i) {
cnt.set(fruits[i], (cnt.get(fruits[i]) || 0) + 1);
for (; cnt.size > 2; ++j) {
cnt.set(fruits[j], cnt.get(fruits[j])! - 1);
if (!cnt.get(fruits[j])) {
cnt.delete(fruits[j]);
}
}
ans = Math.max(ans, i - j + 1);
}
return ans;
}use std::collections::HashMap;
impl Solution {
pub fn total_fruit(fruits: Vec<i32>) -> i32 {
let mut cnt = HashMap::new();
let mut ans = 0;
let mut j = 0;
for (i, &x) in fruits.iter().enumerate() {
*cnt.entry(x).or_insert(0) += 1;
while cnt.len() > 2 {
let y = fruits[j];
j += 1;
*cnt.get_mut(&y).unwrap() -= 1;
if cnt[&y] == 0 {
cnt.remove(&y);
}
}
ans = ans.max(i - j + 1);
}
ans as i32
}
}In Solution 1, we find that the window size sometimes increases and sometimes decreases, which requires us to update the answer each time.
But what this problem actually asks for is the maximum number of fruits, that is, the "largest" window. We don't need to shrink the window, we just need to let the window monotonically increase. So the code omits the operation of updating the answer each time, and only needs to return the size of the window as the answer after the traversal ends.
The time complexity is fruits array.
class Solution:
def totalFruit(self, fruits: List[int]) -> int:
cnt = Counter()
j = 0
for x in fruits:
cnt[x] += 1
if len(cnt) > 2:
y = fruits[j]
cnt[y] -= 1
if cnt[y] == 0:
cnt.pop(y)
j += 1
return len(fruits) - jclass Solution {
public int totalFruit(int[] fruits) {
Map<Integer, Integer> cnt = new HashMap<>();
int j = 0, n = fruits.length;
for (int x : fruits) {
cnt.merge(x, 1, Integer::sum);
if (cnt.size() > 2) {
int y = fruits[j++];
if (cnt.merge(y, -1, Integer::sum) == 0) {
cnt.remove(y);
}
}
}
return n - j;
}
}class Solution {
public:
int totalFruit(vector<int>& fruits) {
unordered_map<int, int> cnt;
int j = 0, n = fruits.size();
for (int& x : fruits) {
++cnt[x];
if (cnt.size() > 2) {
int y = fruits[j++];
if (--cnt[y] == 0) {
cnt.erase(y);
}
}
}
return n - j;
}
};func totalFruit(fruits []int) int {
cnt := map[int]int{}
j := 0
for _, x := range fruits {
cnt[x]++
if len(cnt) > 2 {
y := fruits[j]
cnt[y]--
if cnt[y] == 0 {
delete(cnt, y)
}
j++
}
}
return len(fruits) - j
}function totalFruit(fruits: number[]): number {
const n = fruits.length;
const cnt: Map<number, number> = new Map();
let j = 0;
for (const x of fruits) {
cnt.set(x, (cnt.get(x) || 0) + 1);
if (cnt.size > 2) {
cnt.set(fruits[j], cnt.get(fruits[j])! - 1);
if (!cnt.get(fruits[j])) {
cnt.delete(fruits[j]);
}
++j;
}
}
return n - j;
}use std::collections::HashMap;
impl Solution {
pub fn total_fruit(fruits: Vec<i32>) -> i32 {
let mut cnt = HashMap::new();
let mut j = 0;
let n = fruits.len();
for &x in &fruits {
*cnt.entry(x).or_insert(0) += 1;
if cnt.len() > 2 {
let y = fruits[j];
j += 1;
*cnt.get_mut(&y).unwrap() -= 1;
if cnt[&y] == 0 {
cnt.remove(&y);
}
}
}
(n - j) as i32
}
}