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backtrack_93_restoreIpAddresses.py
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backtrack_93_restoreIpAddresses.py
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"""
给定一个只包含数字的字符串,复原它并返回所有可能的 IP 地址格式。
有效的 IP 地址正好由四个整数(每个整数位于 0 到 255 之间组成),整数之间用 '.' 分隔。
坑:
每段区域不能有前导0: "01", "012", "00", etc.
"""
class Solution:
def restoreIpAddresses(self, s):
""" input| s: str
output| List[str]
"""
n = len(s)
res = []
def backtrack(start, remain, path):
nonlocal res
# terminate
if remain == 0:
# finished placement of 3 dots
if n-start>0 and n-start<=3: # all num has been recorded
cur = s[start:n]
if cur[0]=='0' and len(cur)>1:
return
if int(cur) >= 0 and int(cur) <= 255:
res.append('.'.join(path+[cur]))
return
# make choice
for l in range(1,4):
if start + l <= n: # if not reach end
cur = s[start:start+l]
if cur[0]=='0' and len(cur)>1:
return
if int(cur) >= 0 and int(cur) <= 255:
backtrack(start+l, remain-1, path+[cur])
else:
return
backtrack(0, 3, [])
return res
if __name__=="__main__":
app = Solution()
string = "25525511135"
res = app.restoreIpAddresses(string)
print(res)