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‎Problemset/0918-Maximum Sum Circular Subarray/README.md

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# 918. Maximum Sum Circular Subarray
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Given a **circular integer array** `nums` of length `n`, return *the maximum possible sum of a non-empty **subarray** of* `nums`.
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A **circular array** means the end of the array connects to the beginning of the array. Formally, the next element of `nums[i]` is `nums[(i + 1) % n]` and the previous element of `nums[i]` is `nums[(i - 1 + n) % n]`.
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A **subarray** may only include each element of the fixed buffer `nums` at most once. Formally, for a subarray `nums[i], nums[i + 1], ..., nums[j]`, there does not exist `i <= k1`, `k2 <= j` with `k1 % n == k2 % n`.
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#### Example 1:
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<pre>
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<strong>Input:</strong> nums = [1,-2,3,-2]
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<strong>Output:</strong> 3
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<strong>Explanation:</strong> Subarray [3] has maximum sum 3.
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</pre>
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#### Example 2:
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<pre>
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<strong>Input:</strong> nums = [5,-3,5]
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<strong>Output:</strong> 10
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<strong>Explanation:</strong> Subarray [5,5] has maximum sum 5 + 5 = 10.
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</pre>
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#### Example 3:
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<pre>
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<strong>Input:</strong> nums = [-3,-2,-3]
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<strong>Output:</strong> -2
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<strong>Explanation:</strong> Subarray [-2] has maximum sum -2.
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</pre>
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#### Constraints:
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* `n == nums.length`
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* <code>1 <= n <= 3 * 10<sup>4</sup></code>
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* <code>-3 * 10<sup>4</sup> <= nums[i] <= 3 * 10<sup>4</sup></code>
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## Solutions (Rust)
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### 1. Solution
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```Rust
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impl Solution {
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pub fn max_subarray_sum_circular(nums: Vec<i32>) -> i32 {
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let sum = nums.iter().sum();
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let mut max_sum = nums[0];
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let mut min_sum = nums[0];
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let mut prefix_sum = nums[0];
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let mut ret = nums[0].max(sum);
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for i in 1..nums.len() {
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prefix_sum += nums[i];
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ret = ret
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.max(prefix_sum - min_sum)
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.max(sum - prefix_sum + max_sum);
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max_sum = max_sum.max(prefix_sum);
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min_sum = min_sum.min(prefix_sum);
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}
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ret
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}
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}
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```

‎Problemset/0918-Maximum Sum Circular Subarray/README_CN.md

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# 918. 环形子数组的最大和
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给定一个长度为 `n` 的**环形整数数组** `nums` ，返回 *`nums` 的非空 **子数组** 的最大可能和* 。
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**环形数组** 意味着数组的末端将会与开头相连呈环状。形式上， `nums[i]` 的下一个元素是 `nums[(i + 1) % n]` ， `nums[i]` 的前一个元素是 `nums[(i - 1 + n) % n]` 。
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**子数组** 最多只能包含固定缓冲区 `nums` 中的每个元素一次。形式上，对于子数组 `nums[i], nums[i + 1], ..., nums[j]` ，不存在 `i <= k1, k2 <= j` 其中 `k1 % n == k2 % n` 。
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#### 示例 1:
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<pre>
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<strong>输入:</strong> nums = [1,-2,3,-2]
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<strong>输出:</strong> 3
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<strong>解释:</strong> 从子数组 [3] 得到最大和 3
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</pre>
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#### 示例 2:
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<pre>
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<strong>输入:</strong> nums = [5,-3,5]
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<strong>输出:</strong> 10
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<strong>解释:</strong> 从子数组 [5,5] 得到最大和 5 + 5 = 10
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</pre>
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#### 示例 3:
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<pre>
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<strong>输入:</strong> nums = [3,-2,2,-3]
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<strong>输出:</strong> 3
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<strong>解释:</strong> 从子数组 [3] 和 [3,-2,2] 都可以得到最大和 3
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</pre>
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#### 提示:
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* `n == nums.length`
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* <code>1 <= n <= 3 * 10<sup>4</sup></code>
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* <code>-3 * 10<sup>4</sup> <= nums[i] <= 3 * 10<sup>4</sup></code>
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## 题解 (Rust)
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### 1. 题解
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```Rust
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impl Solution {
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pub fn max_subarray_sum_circular(nums: Vec<i32>) -> i32 {
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let sum = nums.iter().sum();
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let mut max_sum = nums[0];
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let mut min_sum = nums[0];
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let mut prefix_sum = nums[0];
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let mut ret = nums[0].max(sum);
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for i in 1..nums.len() {
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prefix_sum += nums[i];
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ret = ret
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.max(prefix_sum - min_sum)
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.max(sum - prefix_sum + max_sum);
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max_sum = max_sum.max(prefix_sum);
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min_sum = min_sum.min(prefix_sum);
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}
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ret
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}
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}
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```

‎Problemset/0918-Maximum Sum Circular Subarray/Solution.rs

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impl Solution {
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pub fn max_subarray_sum_circular(nums: Vec<i32>) -> i32 {
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let sum = nums.iter().sum();
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let mut max_sum = nums[0];
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let mut min_sum = nums[0];
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let mut prefix_sum = nums[0];
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let mut ret = nums[0].max(sum);
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for i in 1..nums.len() {
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prefix_sum += nums[i];
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ret = ret
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.max(prefix_sum - min_sum)
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.max(sum - prefix_sum + max_sum);
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max_sum = max_sum.max(prefix_sum);
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min_sum = min_sum.min(prefix_sum);
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}
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ret
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}
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}

‎README.md

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[915][915l] |[Partition Array into Disjoint Intervals][915] |![rb]&nbsp;&nbsp;![rs]
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[916][916l] |[Word Subsets][916] |![rb]&nbsp;&nbsp;![rs]
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[917][917l] |[Reverse Only Letters][917] |![py]
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[918][918l] |[Maximum Sum Circular Subarray][918] |![rs]
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[919][919l] |[Complete Binary Tree Inserter][919] |![py]
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[920][920l] |[Number of Music Playlists][920] |![rs]
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[921][921l] |[Minimum Add to Make Parentheses Valid][921] |![rs]
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[915]:Problemset/0915-Partition%20Array%20into%20Disjoint%20Intervals/README.md#915-partition-array-into-disjoint-intervals
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[916]:Problemset/0916-Word%20Subsets/README.md#916-word-subsets
19881989
[917]:Problemset/0917-Reverse%20Only%20Letters/README.md#917-reverse-only-letters
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[918]:Problemset/0918-Maximum%20Sum%20Circular%20Subarray/README.md#918-maximum-sum-circular-subarray
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[919]:Problemset/0919-Complete%20Binary%20Tree%20Inserter/README.md#919-complete-binary-tree-inserter
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[920]:Problemset/0920-Number%20of%20Music%20Playlists/README.md#920-number-of-music-playlists
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[921]:Problemset/0921-Minimum%20Add%20to%20Make%20Parentheses%20Valid/README.md#921-minimum-add-to-make-parentheses-valid
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[915l]:https://leetcode.com/problems/partition-array-into-disjoint-intervals/
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[916l]:https://leetcode.com/problems/word-subsets/
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[917l]:https://leetcode.com/problems/reverse-only-letters/
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[918l]:https://leetcode.com/problems/maximum-sum-circular-subarray/
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[919l]:https://leetcode.com/problems/complete-binary-tree-inserter/
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[920l]:https://leetcode.com/problems/number-of-music-playlists/
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[921l]:https://leetcode.com/problems/minimum-add-to-make-parentheses-valid/

‎README_CN.md

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[915][915l] |[分割数组][915] |![rb]&nbsp;&nbsp;![rs]
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[916][916l] |[单词子集][916] |![rb]&nbsp;&nbsp;![rs]
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[917][917l] |[仅仅反转字母][917] |![py]
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[918][918l] |[环形子数组的最大和][918] |![rs]
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[919][919l] |[完全二叉树插入器][919] |![py]
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[920][920l] |[播放列表的数量][920] |![rs]
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[921][921l] |[使括号有效的最少添加][921] |![rs]
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19861987
[915]:Problemset/0915-Partition%20Array%20into%20Disjoint%20Intervals/README_CN.md#915-分割数组
19871988
[916]:Problemset/0916-Word%20Subsets/README_CN.md#916-单词子集
19881989
[917]:Problemset/0917-Reverse%20Only%20Letters/README_CN.md#917-仅仅反转字母
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[918]:Problemset/0918-Maximum%20Sum%20Circular%20Subarray/README_CN.md#918-环形子数组的最大和
19891991
[919]:Problemset/0919-Complete%20Binary%20Tree%20Inserter/README_CN.md#919-完全二叉树插入器
19901992
[920]:Problemset/0920-Number%20of%20Music%20Playlists/README_CN.md#920-播放列表的数量
19911993
[921]:Problemset/0921-Minimum%20Add%20to%20Make%20Parentheses%20Valid/README_CN.md#921-使括号有效的最少添加
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34073409
[915l]:https://leetcode.cn/problems/partition-array-into-disjoint-intervals/
34083410
[916l]:https://leetcode.cn/problems/word-subsets/
34093411
[917l]:https://leetcode.cn/problems/reverse-only-letters/
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[918l]:https://leetcode.cn/problems/maximum-sum-circular-subarray/
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[919l]:https://leetcode.cn/problems/complete-binary-tree-inserter/
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[920l]:https://leetcode.cn/problems/number-of-music-playlists/
34123415
[921l]:https://leetcode.cn/problems/minimum-add-to-make-parentheses-valid/

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