LintCode "Maximum Subarray Difference"

class Solution {
    void largest_l2r(vector<int> &A, vector<int> &ret)
    {
    size_t len = A.size();
    ret.resize(len);
    
    int csum = A[0], sofar = A[0];
    
    ret[0] = A[0];    
    for (int i = 1; i < len; i++)
    {
        int nsum = csum + A[i];
        if (A[i] > nsum)
        {
        csum = A[i];
        }
        else
        {
        csum = nsum;
        }
        sofar = max(sofar, csum);
        ret[i] = sofar;
    }
    }
    void smallest_l2r(vector<int> &A, vector<int> &ret)
    {
    size_t len = A.size();
    ret.resize(len);
    
    int csum = A[0], sofar = A[0];
    
    ret[0] = A[0];    
    for (int i = 1; i < len; i++)
    {
        int nsum = csum + A[i];
        if (A[i] < nsum)
        {
        csum = A[i];
        }
        else
        {
        csum = nsum;
        }
        sofar = min(sofar, csum);
        ret[i] = sofar;
    }
    }
    void largest_r2l(vector<int> &A, vector<int> &ret)
    {
    size_t len = A.size();
    ret.resize(len);
    
    int csum = A.back(), sofar = A.back();
    
    ret[len - 1] = A.back();    
    for (int i = len - 2; i >= 0; i --)
    {
        int nsum = csum + A[i];
        if (A[i] > nsum)
        {
        csum = A[i];
        }
        else
        {
        csum = nsum;
        }
        sofar = max(sofar, csum);
        ret[i] = sofar;
    }
    }
    void smallest_r2l(vector<int> &A, vector<int> &ret)
    {
    size_t len = A.size();
    ret.resize(len);
    
    int csum = A.back(), sofar = A.back();
    
    ret[len - 1] = A.back();    
    for (int i = len - 2; i >= 0; i --)
    {
        int nsum = csum + A[i];
        if (A[i] < nsum)
        {
        csum = A[i];
        }
        else
        {
        csum = nsum;
        }
        sofar = min(sofar, csum);
        ret[i] = sofar;
    }
    }
public:
    /**
     * @param nums: A list of integers
     * @return: An integer indicate the value of maximum difference between two
     *          Subarrays
     */
    int maxDiffSubArrays(vector<int> nums) {
        vector<int> max_l2r, max_r2l;
    largest_l2r(nums, max_l2r);
    largest_r2l(nums, max_r2l);
    
    vector<int> min_l2r, min_r2l;
    smallest_l2r(nums, min_l2r);
    smallest_r2l(nums, min_r2l);
    
    int ret = INT_MIN;
    for(int i = 0; i < nums.size() - 1; i ++)
    {
        int r1 = max_l2r[i] - min_r2l[i + 1];
        int r2 = max_r2l[i + 1] - min_l2r[i];
        ret = max(ret, max(r1, r2));
    }
    return ret;
    }
};