918. 环形子数组的最大和

 

//数组是连续的
class Solution 
{
public:
    int maxSubarraySumCircular(vector<int>& A) 
    {
        // 单调队列
        int n = A.size();
        deque<int> q;
        for(int i = 0; i < n; i++) A.push_back(A[i]);
        vector<int> s(2 * n + 1);
        // 计算前缀和
        
        for(int i = 1; i <= 2 * n; i++)
        {
            s[i] = s[i- 1] + A[i-1];
        }
        // 初始化队列
        q.push_back(0);
        int res = INT_MIN;
    
        for(int i = 1; i <= 2 * n; i++)
        {
            if(q.size() && i - n > q.front()) q.pop_front();
            if(q.size()) res = max(res, s[i] - s[q.front()]);
            while(q.size() && s[q.back()] > s[i]) q.pop_back();
            q.push_back(i);
        }
        return res;
    }
};