# Task
 You are given two string `a` an `s`. Starting with an empty string we can do the following two operations:
```
append the given string a to the end of the current string.
erase one symbol of the current string.```
Your task is to find the least number of operations needed to construct the given string s. Assume that all the letters from `s` appear in `a` at least once.

# Example

 For `a = "aba", s = "abbaab"`, the result should be `6`.
 
 Coinstruction:
 
 `"" -> "aba" -> "ab" -> "ababa" -> "abba" -> "abbaaba" -> "abbaab".`
 
 So, the result is 6.

 For `a = "aba", s = "a"`, the result should be `3`.
 
 Coinstruction:
 
 `"" -> "aba" -> "ab" -> "a".`
 
 So, the result is 3.

 For `a = "aba", s = "abaa"`, the result should be `4`.
 
 Coinstruction:
 
 `"" -> "aba" -> "abaaba" -> "abaab" -> "abaa".`
 
 So, the result is 4.

# Input/Output


 - `[input]` string `a`

  string to be appended. Contains only lowercase English letters. 
  
  1 <= a.length <= 20


 - `[input]` string `s`

  desired string containing only lowercase English letters.
  
  1 <= s.length < 1000


 - `[output]` an integer

  minimum number of operations

Difficulty: EASY
Starter code: def string_constructing(a, s):
	

Solutions:
def string_constructing(a, s):
	if len(s) == 0:
		return 0
	i = -1
	for (j, c) in enumerate(s):
		i = a.find(c, i + 1)
		if i < 0 or i == len(a) - 1:
			break
	return len(a) - j + (i < 0) + string_constructing(a, s[j + (i >= 0):])


def string_constructing(pattern, target):
	pattern = list(pattern)
	target = list(target) + [None]
	buffer = [None]
	pos = 0
	count = 0
	while True:
		if target[pos] == buffer[pos]:
			if target[pos] == None:
				return count
			pos += 1
		elif buffer[pos] == None:
			buffer[-1:-1] = pattern
			count += 1
		else:
			del buffer[pos]
			count += 1
	return count


import re

def string_constructing(a, s):
	n = len(re.findall('?'.join(list(a)) + '?', s)) - 1
	return n + len(a) * n - len(s)


def string_constructing(a, s):
	i = 0
	for c in s:
		while a[i % len(a)] != c:
			i += 1
		i += 1
	return (i + len(a) - 1) // len(a) * (len(a) + 1) - len(s)


def string_constructing(a, s):
	(i, r) = (0, 1)
	for x in s:
		y = a[i % len(a)]
		while x != y:
			r += 1
			i += 1
			y = a[i % len(a)]
		i += 1
	return r + i // len(a) + -i % len(a) - (i % len(a) == 0)


def string_constructing(a, s):
	current = ''
	step = 0
	while current != s:
		for i in range(len(current)):
			if i >= len(s):
				return step + len(current) - len(s)
			if current[i] != s[i]:
				current = current[i + 1:]
				s = s[i:]
				break
		else:
			current += a
		step += 1
	return step


def string_constructing(a, s):
	T = a
	(c, al) = (1, 0)
	while T != s:
		if al < len(T) and al < len(s) and (T[al] == s[al]):
			al += 1
		elif al == len(T):
			T += a
			c += 1
		elif len(s) < len(T) or T[al] != s[al]:
			T = T[:al] + T[al + 1:]
			al = max(al - 1, 0)
			c += 1
	return c


def common_len(s1, s2):
	(n, m) = (len(s1), len(s2))
	i = 0
	for c1 in s1:
		if i >= len(s2):
			break
		elif c1 == s2[i]:
			i += 1
	return i

def string_constructing(a, s):
	r = []
	c = 0
	p = 0
	while p < len(s):
		l = common_len(a, s[p:p + len(a)])
		c += 1 + len(a) - l
		p += l
	return c


def string_constructing(a, b):
	(s, c) = ([], 0)
	while ''.join(s) != b:
		s.extend(list(a))
		c += 1
		i = 0
		while i < len(s) and i < len(b):
			if s[i] == b[i]:
				i += 1
			else:
				c += 1
				s.pop(i)
		if ''.join(s).startswith(b):
			c += len(s[len(b):])
			break
	return c


def string_constructing(a, s):
	if not s:
		return 0
	if set(s) - set(a):
		return False
	n = 1
	i = 0
	for c in s:
		while True:
			if i == len(a):
				i = 0
				n += 1
			if a[i] != c:
				n += 1
				i += 1
			else:
				i += 1
				break
	return n + len(a) - i