28天【代码随想录算法训练营34期】第七章 回溯算法 (● 93.复原IP地址 ● 78.子集 ● 90.子集II )

93.复原IP地址

class Solution:
    def restoreIpAddresses(self, s: str) -> List[str]:
        result = []
        self.backtracking(s, [], 0, result)
        return result
    
    def backtracking(self, s, path, index, result):
        if index >= len(s) and len(path) == 4:
            result.append('.'.join(path))
            return
        if len(path) > 4:
            return
        for i in range(index, min(index+3, len(s))):
            if self.is_valid(s, index, i):
                sub = s[index:i+1]
                path.append(sub)
                self.backtracking(s, path, i+1, result)
                path.pop()

    def is_valid(self, s, start, end):
        if start > end:
            return False
        if s[start] == '0' and start != end:
            return False
        num = int(s[start:end+1])
        return 0 <= num and num <= 255

78.子集

class Solution:
    def subsets(self, nums: List[int]) -> List[List[int]]:
        result = [[]]
        self.backtracking(nums, [], 0, result)
        return result
    def backtracking(self, nums, path, index, result):
        if index >= len(nums):
            return
        for i in range(index, len(nums)):
            path.append(nums[i])
            result.append(path[:])
            self.backtracking(nums, path, i+1, result)
            path.pop()
        

90.子集II

class Solution:
    def subsetsWithDup(self, nums: List[int]) -> List[List[int]]:
        nums.sort()
        result = [[]]
        self.backtracking(nums, [], 0, result)
        return result
    def backtracking(self, nums, path, index, result):
        if index >= len(nums):
            return
        for i in range(index, len(nums)):
            if index != i and nums[i] == nums[i-1]:
                continue
            path.append(nums[i])
            result.append(path[:])
            self.backtracking(nums, path, i+1, result)
            path.pop()