lintcode-medium-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.

Notice

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

.

Challenge

Can you do it in time complexity O(n) ?

public class Solution {
/**
* @param nums: A list of integers
* @return: An integer denotes the sum of max two non-overlapping subarrays
*/
public int maxTwoSubArrays(ArrayList<Integer> nums) {
// write your code

if(nums == null || nums.size() == 0)
return 0;

int size = nums.size();

int sum = nums.get(0);
int[] l2r = new int[size];
int[] r2l = new int[size];
l2r[0] = nums.get(0);
r2l[size - 1] = nums.get(size - 1);

for(int i = 1; i < size; i++){
if(sum < 0)
sum = 0;

sum += nums.get(i);

if(sum > l2r[i - 1])
l2r[i] = sum;
else
l2r[i] = l2r[i - 1];
}

sum = nums.get(size - 1);

for(int i = size - 2; i >= 0; i--){
if(sum < 0)
sum = 0;

sum += nums.get(i);

if(sum > r2l[i + 1])
r2l[i] = sum;
else
r2l[i] = r2l[i + 1];
}

int result = Integer.MIN_VALUE;

for(int i = 0; i < size - 1; i++)
result = Math.max(result, l2r[i] + r2l[i + 1]);

return result;
}
}