/// <summary>
/// T (nlogn) S O(1)
/// </summary>
/// <param name="arr"></param>
/// <param name="start"></param>
/// <param name="end"></param>
/// <returns></returns>
private static MaxSubArray MaxSumSubArrayRecursion(int[] arr, int start, int end)
{
if (start == end)
{
return(new MaxSubArray()
{
start = start, end = end, val = arr[start]
});
}
if (start > end)
{
return(new MaxSubArray());
}
int mid = start + (end - start) / 2;
MaxSubArray left = MaxSumSubArrayRecursion(arr, start, mid - 1);
MaxSubArray right = MaxSumSubArrayRecursion(arr, mid + 1, end);
MaxSubArray middle = GetMaxMiddle(arr, start, end, mid);
// find the max of left right and middle.f
MaxSubArray max = left.val < right.val ? right : left;
max = max.val < middle.val ? middle : max;
return(max);
}
/// <summary>
/// T: O(n^3) S: O(1)
/// </summary>
/// <param name="arr"></param>
/// <returns></returns>
private static MaxSubArray MaxSumSubArrayBF(int[] arr)
{
MaxSubArray result = new MaxSubArray();
for (int start = 0; start < arr.Length; start++)
{
for (int end = start; end < arr.Length; end++)
{
int value = 0;
for (int i = start; i <= end; i++)
{
value += arr[i];
}
if (value > result.val)
{
result.start = start;
result.end = end;
result.val = value;
}
}
}
return(result);
}
/// <summary>
/// T: O(n^2) S: O(1)
/// </summary>
/// <param name="arr"></param>
/// <returns></returns>
private static MaxSubArray MaxSumSubArrayBFImproved(int[] arr)
{
MaxSubArray result = new MaxSubArray();
for (int start = 0; start < arr.Length; start++)
{
int cumSum = 0;
for (int end = start; end < arr.Length; end++)
{
cumSum += arr[end];
if (cumSum > result.val)
{
result.start = start;
result.end = end;
result.val = cumSum;
}
}
}
return(result);
}
