//just playing for fun
public static SubArrayResult maxsubArrayWithIndexMethod2(int[] array)
{
SubArrayResult result = new SubArrayResult();
int maxsum = Int32.MinValue;
int runningsum = 0;
StringBuilder sbIndexrunning = new StringBuilder();
StringBuilder maxIndexstring = new StringBuilder();
for (int i = 0; i < array.Length; i++)
{
runningsum = runningsum + array[i];
sbIndexrunning.Append(i).Append(',');
if (runningsum > maxsum)
{
maxsum = runningsum;
maxIndexstring = sbIndexrunning;
}
if (runningsum < 0)
{
runningsum = 0;
sbIndexrunning.Clear();
}
}
if (maxIndexstring.Length > 0)
{
result.Sum = maxsum;
string[] maxvalues = maxIndexstring.ToString().TrimEnd(',').Split(',');
result.StartIndex = Convert.ToInt32(maxvalues[0]);
result.EndIndex = Convert.ToInt32(maxvalues[maxvalues.Length - 1]);
}
return(result);
}
//Kadane’s algorithm for 1D array
public static SubArrayResult maxsubArrayWithIndex(int[] array)
{
int maxsum = Int32.MinValue;
int runningsum = 0;
List <int> runningindexlist = new List <int>();
List <int> maxindexlist = null;
SubArrayResult result = null;
for (int i = 0; i < array.Length; i++)
{
runningsum = runningsum + array[i];
runningindexlist.Add(i);
if (runningsum > maxsum)
{
maxsum = runningsum;
maxindexlist = new List <int>(runningindexlist);
}
//reset sum to 0 when the sum value is negative
if (runningsum < 0)
{
runningsum = 0;
runningindexlist.Clear();
}
}
if (maxindexlist.Count > 0)
{
result = new SubArrayResult();
result.Sum = maxsum;
result.StartIndex = maxindexlist[0];
result.EndIndex = maxindexlist[maxindexlist.Count - 1];
}
return(result);
}
public static MatrixSubArrayResult MaxSubMatrixWithIndex(int[,] matrix)
{
int rowcount = matrix.GetLength(0);
int colcount = matrix.GetLength(1);
int[] partialsum = new int[colcount]; //size of colum
int maxsum = Int32.MinValue;
MatrixSubArrayResult result = new MatrixSubArrayResult();
//test
List <String> test = new List <string>();
// 1 2 -1
//-3 -1 -4
// 1 -5 2
// get all possible rows..
//Now in this 3 x 3 matrix, the row can be grouped as [1],[1,2],[1,2,3],[2],[2,3],[3].
for (int rowstart = 0; rowstart < rowcount; rowstart++)
{
ClearArray(partialsum);
for (int rowend = rowstart; rowend < rowcount; rowend++)
{
//here we will get all possible row grouping
//For the given row range ( 1 to 1 or 1 -3) we sum the col value
//p[0] will be the sum of first col
//p[1] will be the sume of secon col
//p[columcount -1]
//Important note: here we don't clear the array in this iteration
//becoze row of 1 result will be added to row of 2 and then three..
//we clear it only after the master loop value changes
for (int i = 0; i < colcount; i++)
{
//This is an important piece..what we do is
//for [1 t0 1] row p[0] = 1 p[1] = 2 p[2] = -1
partialsum[i] = partialsum[i] + matrix[rowend, i];
}
//StringBuilder sb = new StringBuilder();
////testing
//for (int j = 0; j < partialsum.Length; j++)
//{
// sb.Append(partialsum[j]).Append(',');
//}
//test.Add(sb.ToString());
//here we can play with co-ordinates
SubArrayResult infores = maxsubArrayWithIndex(partialsum);
if (infores != null && infores.Sum > maxsum)
{
//maxsum = sum;
maxsum = infores.Sum;
result.Sum = infores.Sum;
result.RowStart = rowstart;
result.RowEnd = rowend;
result.ColStart = infores.StartIndex;
result.ColEnd = infores.EndIndex;
}
}
}
return(result);
}
