Longest SharedSubstring Solution

#Ryan Sickles longesSharedSubstring Solution
#Should have a O(n**2)

def longestSharedSubstring(stringOne,stringTwo):
	substringMatrix = [[len(stringOne)],[len(stringTwo)]] #creates a row and column matrix with the number of cols and rows based on size of strings
	largest_subString = 0 #length of the largest substring
	largest_loc_row = 0 #row index of longest substring in matrix
	largest_loc_col = 0 #column index of longest subtring in matrix
	longestString = "" #the longest substring 
	for row in xrange(len(stringOne)):
		for column in xrange(len(stringTwo)):
			s1 = stringOne[row] #char in string1
			s2 = substringMatrix[column] #char in string2
			if(s1==s1): #if chars are equal to eachother
				if((row==0 or col==0) or isPartOfSubstring(row,column,substringMatrix)): #if they are in row 0 or if the match is part of substring 
					if (row==0):
						newIndex = 1
					else:
						newIndex = substringMatrix[row-1][col-1] + 1 #increase size of found substring by 1
					substringMatrix[row][column] = newIndex #adds an index value to the index before it
					if(newIndex > largest_subString): #if the size found substring is longer than the previously found substring length
						largest_loc_row = row #sets biggest substring so far to new matrix location
						largest_loc_col = col
						largest_subString = newIndex #longest substring is highest substring count
			else:
				substringMatrix = [row][column] = 0 #if the chars are not equal put a 0 
	while(longest_loc_row>=0 and longest_loc_col>=0): #finds the substring of the substring match that is the longest
		longestString+=substringMatrix[longest_loc_row][longest_loc_col]
		longest_loc_row-=1
		longest_loc_col-=1
	return longestString

def isPartOfSubstring(row,col,matrix): #checks to see if if the character is at the end of a previous substring
	while(row>=0 and col>=0):
		row-=1 #checks along diagonal in matrix
		col-=1
		if(matrix[row][col]==0): #if the previous chars are not equal then this new match is not part of a substring
			return False
	return True

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