Restore IP Addresses — LeetCode 93 Python Solution
MediumStringBacktracking
- Problem
- #93
- Pattern
- Backtracking
- Reading time
- 4 min
- Source
- leetcode.com
The problem
A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros.
Example
- Input
- s = "25525511135"
- Output
- ["255.255.11.135","255.255.111.35"]
Python solution
Python
class Solution:
def restoreIpAddresses(self, s: str) -> List[str]:
def check(i: int, j: int) -> int:
if s[i] == "0" and i != j:
return False
return 0 <= int(s[i : j + 1]) <= 255
def dfs(i: int):
if i >= n and len(t) == 4:
ans.append(".".join(t))
return
if i >= n or len(t) >= 4:
return
for j in range(i, min(i + 3, n)):
if check(i, j):
t.append(s[i : j + 1])
dfs(j + 1)
t.pop()
n = len(s)
ans = []
t = []
dfs(0)
return ansComplexity
| Measure | Complexity |
|---|---|
| Time | O(n \times 3^4) |
| Space | O(n) auxiliary |
Pattern: Backtracking
Build candidates one choice at a time and abandon a branch the moment it cannot work. LeetCode 93. Restore IP Addresses is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Backtracking.
The backtracking guide has the Python template for the pattern and the 105 LeetCode problems that use it.
Related problems
Frequently asked questions
- How hard is LeetCode 93. Restore IP Addresses?
- LeetCode 93. Restore IP Addresses is rated Medium on LeetCode.
- What is the time complexity of LeetCode 93. Restore IP Addresses?
- The Python solution on this page runs in O(n \times 3^4).
- What is the space complexity of LeetCode 93. Restore IP Addresses?
- The Python solution on this page uses O(n) auxiliary space.
- What topics does LeetCode 93. Restore IP Addresses cover?
- LeetCode 93. Restore IP Addresses is tagged String and Backtracking on LeetCode.