918.Maximum Sum Circular Subarray

tags: Medium,Array,DP,Divide and Conquer,Queue

918. Maximum Sum Circular Subarray

題目描述

Given a circular integer array nums of length n, return the maximum possible sum of a non-empty subarray of nums.

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].

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.

範例

Example 1:

Input: nums = [1,-2,3,-2]
Output: 3
Explanation: Subarray [3] has maximum sum 3.

Example 2:

Input: nums = [5,-3,5]
Output: 10
Explanation: Subarray [5,5] has maximum sum 5 + 5 = 10.

Example 3:

Input: nums = [-3,-2,-3]
Output: -2
Explanation: Subarray [-2] has maximum sum -2.

Constraints:

• n == nums.length
• 1 <= n <= 3 * 10⁴
• -3 * 10⁴ <= nums[i] <= 3 * 10⁴

解答

C++

class Solution {
public:
    int maxSubarraySumCircular(vector<int>& nums) {
        int curMax = INT_MIN, maxSum = 0, curMin = INT_MAX, minSum = 0, total = 0;
        for (auto n : nums) {
            maxSum = max(maxSum, 0) + n;
            curMax = max(curMax, maxSum);
            minSum = min(minSum, 0) + n;
            curMin = min(curMin, minSum);
            total += n;
        }
        return curMax > 0 ? max(curMax, total - curMin) : curMax;
    }
};

Yen-Chi ChenThu, Jan 19, 2023

Reference

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