forked from keon/algorithms
/
generate_strobogrammtic.py
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generate_strobogrammtic.py
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"""
A strobogrammatic number is a number that looks
the same when rotated 180 degrees (looked at upside down).
Find all strobogrammatic numbers that are of length = n.
For example,
Given n = 2, return ["11","69","88","96"].
"""
def gen_strobogrammatic(n):
"""
:type n: int
:rtype: List[str]
"""
result = helper(n, n)
return result
def helper(n, length):
if n == 0:
return [""]
if n == 1:
return ["1", "0", "8"]
middles = helper(n-2, length)
result = []
for middle in middles:
if n != length:
result.append("0" + middle + "0")
result.append("8" + middle + "8")
result.append("1" + middle + "1")
result.append("9" + middle + "6")
result.append("6" + middle + "9")
return result
def strobogrammaticInRange(low, high):
"""
:type low: str
:type high: str
:rtype: int
"""
res = []
count = 0
for i in range(len(low), len(high)+1):
res.extend(helper2(i, i))
for perm in res:
if len(perm) == len(low) and int(perm) < int(low):
continue
elif len(perm) == len(high) and int(perm) > int(high):
continue
else:
count += 1
return count
def helper2(self, n, length):
if n == 0:
return [""]
if n == 1:
return ["0", "8", "1"]
mids = helper(n-2, length)
res = []
for mid in mids:
if n != length:
res.append("0"+mid+"0")
res.append("1"+mid+"1")
res.append("6"+mid+"9")
res.append("9"+mid+"6")
res.append("8"+mid+"8")
return res