LeetCode 918. Maximum Sum Circular Subarray

 918. Maximum Sum Circular Subarray

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.

 

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

	class Solution {
	public:
	int maxSubarraySumCircular(vector<int>& nums) {
	int n = nums.size();
	// find min & max sub array
	int min_sum = nums[0];
	int min_pre = nums[0];
	int max_sum = nums[0];
	int max_pre = nums[0];
	for(int i = 1; i < n; i++){
	// min
	int min_cur = min(min_pre + nums[i], nums[i]);
	min_pre = min_cur;
	min_sum = min(min_sum, min_cur);
	// max
	int max_cur = max(max_pre + nums[i], nums[i]);
	max_pre = max_cur;
	max_sum = max(max_sum, max_cur);
	}
	// sum
	int sum = 0;
	for(auto x: nums)
	sum += x;
	return sum == min_sum ? max_sum : max(max_sum, sum - min_sum);
	}
	};

view raw 918. Maximum Sum Circular Subarray.cpp hosted with ❤ by GitHub