LintCode: Maximum Subarray II

Given an array of integers, find two non-overlapping subarrays which have the largest sum.
The number in each subarray should be contiguous.
Return the largest sum.

Note

The subarray should contain at least one number

Example

For given [1, 3, -1, 2, -1, 2], the two subarrays are [1, 3] and [2, -1, 2] or [1, 3, -1, 2] and [2], they both have the largest sum 7.

 
class Solution {
public:
    /**
     * @param nums: A list of integers
     * @return: An integer indicate the value of maximum difference between two
     *          Subarrays
     */
    int maxTwoSubArrays(vector<int> nums) {
        int n = nums.size();
        vector<int> maxLR(n, nums[0]);
        vector<int> maxRL(n, nums[n-1]);
       
        int prev = nums[0];
        for(int i = 1; i< n; i++)
        {
           int sum = nums[i] + (prev >0? prev : 0);
           prev = sum;
           maxLR[i] = max(sum, maxLR[i-1]);
        }
        prev = nums[n-1];
        for(int i = n-2; i>=0; i--) {
           int sum = nums[i] + (prev >0? prev : 0);
           prev = sum;
           maxRL[i] = max(sum, maxRL[i+1]);
        }
        int maxSum = INT_MIN;
        for(int i = 0; i < n-1; i++)
           maxSum = max(maxSum, maxLR[i]+maxRL[i+1]);
       
        return maxSum;
    }
};