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‎README.adoc

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@@ -6451,14 +6451,14 @@ TIP: **公众号的微信号是: `jikerizhi`**。__因为众所周知的原因
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//|{doc_base_url}/0917-reverse-only-letters.adoc[题解]
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//|Easy
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//|
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//
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//|{counter:codes}
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//|{leetcode_base_url}/maximum-sum-circular-subarray/[918. Maximum Sum Circular Subarray^]
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//|{source_base_url}/_0918_MaximumSumCircularSubarray.java[Java]
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//|{doc_base_url}/0918-maximum-sum-circular-subarray.adoc[题解]
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//|Medium
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//
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|{counter:codes}
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|{leetcode_base_url}/maximum-sum-circular-subarray/[918. Maximum Sum Circular Subarray^]
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|{source_base_url}/_0918_MaximumSumCircularSubarray.java[Java]
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|{doc_base_url}/0918-maximum-sum-circular-subarray.adoc[题解]
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|Medium
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|
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//|{counter:codes}
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//|{leetcode_base_url}/complete-binary-tree-inserter/[919. Complete Binary Tree Inserter^]
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//|{source_base_url}/_0919_CompleteBinaryTreeInserter.java[Java]

‎docs/0918-maximum-sum-circular-subarray.adoc

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[#0918-maximum-sum-circular-subarray]
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= 918. Maximum Sum Circular Subarray
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= 918. 环形子数组的最大和
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{leetcode}/problems/maximum-sum-circular-subarray/[LeetCode - Maximum Sum Circular Subarray^]
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https://leetcode.cn/problems/maximum-sum-circular-subarray/[LeetCode - 918. 环形子数组的最大和 ^]
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Given a *circular array* *C* of integers represented by `A`, find the maximum possible sum of a non-empty subarray of *C*.
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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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Here, a _circular array_ means the end of the array connects to the beginning of the array. (Formally, `C[i] = A[i]` when `0 <= i < A.length`, and `C[i+A.length] = C[i]` when `i >= 0`.)
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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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Also, a subarray may only include each element of the fixed buffer `A` at most once. (Formally, for a subarray `C[i], C[i+1], ..., C[j]`, there does not exist `i <= k1, k2 <= j` with `k1 % A.length = k2 % A.length`.)
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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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....
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输入：nums = [1,-2,3,-2]
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输出：3
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解释：从子数组 [3] 得到最大和 3
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....
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*Example 1:*
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[subs="verbatim,quotes,macros"]
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----
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*Input:* [1,-2,3,-2]
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*Output:* 3
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*Explanation:* Subarray [3] has maximum sum 3
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----
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*Example 2:*
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[subs="verbatim,quotes,macros"]
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----
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*Input:* [5,-3,5]
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*Output:* 10
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*Explanation:* Subarray [5,5] has maximum sum 5 + 5 = 10
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----
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*Example 3:*
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[subs="verbatim,quotes,macros"]
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----
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*Input:* [3,-1,2,-1]
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*Output:* 4
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*Explanation:* Subarray [2,-1,3] has maximum sum 2 + (-1) + 3 = 4
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----
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*示例 2：*
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....
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输入：nums = [5,-3,5]
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输出：10
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解释：从子数组 [5,5] 得到最大和 5 + 5 = 10
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....
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*Example 4:*
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*示例 3：*
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[subs="verbatim,quotes,macros"]
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----
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*Input:* [3,-2,2,-3]
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*Output:* 3
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*Explanation:* Subarray [3] and [3,-2,2] both have maximum sum 3
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----
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*Example 5:*
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[subs="verbatim,quotes,macros"]
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----
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*Input:* [-2,-3,-1]
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*Output:* -1
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*Explanation:* Subarray [-1] has maximum sum -1
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----
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*Note: *
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. `-30000 <= A[i] <= 30000`
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. `1 <= A.length <= 30000`
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....
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输入：nums = [3,-2,2,-3]
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输出：3
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解释：从子数组 [3] 和 [3,-2,2] 都可以得到最大和 3
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....
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*提示：*
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* `+n == nums.length+`
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* `1 \<= n \<= 3 * 10^4^`
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* `-3 * 10^4^ \<= nums[i] \<= 3 * 10^4^`
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== 思路分析
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image::images/0918-10.png[{image_attr}]
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[[src-0918]]
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[tabs]
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====
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一刷::
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+
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--
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[{java_src_attr}]
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----
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include::{sourcedir}/_0918_MaximumSumCircularSubarray.java[tag=answer]
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----
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--
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// 二刷::
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// +
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// --
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// [{java_src_attr}]
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// ----
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// include::{sourcedir}/_0918_MaximumSumCircularSubarray_2.java[tag=answer]
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// ----
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// --
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====
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== 参考资料
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. https://leetcode.cn/problems/maximum-sum-circular-subarray/solutions/2350660/huan-xing-zi-shu-zu-de-zui-da-he-by-leet-elou/[918. 环形子数组的最大和 - 官方题解^]
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. https://leetcode.cn/problems/maximum-sum-circular-subarray/solutions/2351107/mei-you-si-lu-yi-zhang-tu-miao-dong-pyth-ilqh/[918. 环形子数组的最大和 - 没有思路？一张图秒懂！^]

‎docs/images/0918-10.png

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‎docs/index.adoc

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include::0918-maximum-sum-circular-subarray.adoc[leveloffset=+1]
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‎logbook/202503.adoc

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|{doc_base_url}/1839-longest-substring-of-all-vowels-in-order.adoc[题解]
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|✅ 滑动窗口。题目不难，只是处理边界条件麻烦。另外，也有取巧解法，可以探索一下。
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|{counter:codes2503}
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|{leetcode_base_url}/maximum-sum-circular-subarray/[918. 环形子数组的最大和^]
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|{doc_base_url}/0918-maximum-sum-circular-subarray.adoc[题解]
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|❌ 理解错题目了。前大，中小，后大，这类子数组也可以产生更多的子数组和。另有“取反”和单调栈解法。
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|===
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截止目前，本轮练习一共完成 {codes2503} 道题。

‎src/main/java/com/diguage/algo/leetcode/_0918_MaximumSumCircularSubarray.java

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package com.diguage.algo.leetcode;
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public class _0918_MaximumSumCircularSubarray {
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// tag::answer[]
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/**
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* @author D瓜哥 · https://www.diguage.com
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* @since 2025-05-14 16:27:15
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*/
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public int maxSubarraySumCircular(int[] nums) {
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int length = nums.length;
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int[] leftSumMax = new int[length];
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leftSumMax[0] = nums[0];
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int leftSum = nums[0];
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int result = nums[0];
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int preMax = nums[0];
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for (int i = 1; i < length; i++) {
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preMax = Math.max(preMax + nums[i], nums[i]);
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result = Math.max(result, preMax);
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leftSum += nums[i];
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leftSumMax[i] = Math.max(leftSumMax[i - 1], leftSum);
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}
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int rightMaxSum = 0;
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for (int i = length - 1; i > 0; i--) {
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rightMaxSum += nums[i];
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result = Math.max(result, rightMaxSum + leftSumMax[i - 1]);
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}
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return result;
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}
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// end::answer[]
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public static void main(String[] args) {
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new _0918_MaximumSumCircularSubarray()
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.maxSubarraySumCircular(new int[]{5, -3, 5});
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}
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}

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