leetcode1186 Maximum Subarray Sum with One Deletion

思路：

最大子段和的变体，前后两个方向分别扫一遍即可。

实现：

 class Solution
 {
 public:
     int maximumSum(vector<int>& arr)
     {
         int n = arr.size();
         if (n == ) return arr[];
         vector<int> f(n), b(n);
         int minn = , sum = ;
         for (int i = ; i < n; i++)
         {
             sum += arr[i];
             f[i] = sum - minn;
             minn = min(minn, sum);
         }
         minn = sum = ;
         for (int i = n - ; i >= ; i--)
         {
             sum += arr[i];
             b[i] = sum - minn;
             minn = min(minn, sum);
         }
         int ans = *max_element(f.begin(), f.end());
         for (int i = ; i < n; i++)
         {
             if (arr[i] > ) continue;
             ans = max(ans, (i >  ? f[i - ] : ) + (i < n -  ? b[i + ] : ));
         }
         return ans;
     }
 }