maximum-sum-of-two-non-overlapping-subarrays

class Solution {
public:
    int try_this (vector<int>& A, int L, int M)
    {
        int res = -1;
        int sz = A.size();
        vector <int> lsum (sz,0);
        vector <int> mxlsum(sz,0);

        lsum[0] = A[0];
        mxlsum[0] = A[0];
        for (int i = 1 ; i < sz ; i ++ )
        {
            lsum[i] = lsum[i -1] + A[i] - (i >= L ? A[i-L] : 0);
            mxlsum[i] = max (mxlsum[i-1], lsum[i]);
        }
        vector <int> rsum (sz,0);
        vector <int> mxrsum (sz,0);

        rsum[sz - 1] = 0;
        mxrsum[sz - 1] = 0;

        for (int i = sz - 2 ; i >= 0 ; i--)
        {
            rsum[i] = rsum[i+1] + A[i+1] - (i+M+1 < sz ? A[i+M+1] : 0);
            mxrsum[i] = max (mxrsum[i+1], rsum[i]);

            res = max (res,mxrsum[i] + mxlsum[i] );
        }
        return res ;
    }

    int maxSumTwoNoOverlap(vector<int>& A, int L, int M) {

      return max (try_this(A,L,M), try_this(A,M,L));


    }
};