Longest Consecutive Subsequence

# Python program to find longest contiguous subsequence
 
 
def findLongestConseqSubseq(arr, n):
 
	s = set()
	ans = 0
 
	# Hash all the array elements
	for ele in arr:
		s.add(ele)
 
	# check each possible sequence from the start
	# then update optimal length
	for i in range(n):
 
		# if current element is the starting
		# element of a sequence
		if (arr[i]-1) not in s:
 
			# Then check for next elements in the
			# sequence
			j = arr[i]
			while(j in s):
				j += 1
 
			# update optimal length if this length
			# is more
			ans = max(ans, j-arr[i])
	return ans
 
 
# Driver code
if __name__ == '__main__':
	n = 7
	arr = [1, 9, 3, 10, 4, 20, 2]
	print("Length of the Longest contiguous subsequence is ",
		findLongestConseqSubseq(arr, n))