代码随想训练营第二十七天（Python）｜ 39. 组合总和、40.组合总和II、131.分割回文串

39. 组合总和

class Solution:
    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
        res = []
        candidates.sort()
        self.tracebacking(candidates, target, 0, 0, [], res)
        return res

    def tracebacking(self, candidates, target, total, start, path, res):
        if total == target:
            res.append(path[:])
            return

        for i in range(start, len(candidates)):
            if total + candidates[i] > target:
                break
            path.append(candidates[i])
            total += candidates[i]
            self.tracebacking(candidates, target, total, i, path, res)
            total -= candidates[i]
            path.pop()

40.组合总和II

class Solution:
    def combinationSum2(self, candidates: List[int], target: int) -> List[List[int]]:
        res = []
        candidates.sort()
        self.tracebacking(candidates, target, 0, 0, [], res)
        return res

    def tracebacking(self, candidates, target, total, start, path, res):
        if target == total:
            res.append(path[:])
            return

        # 横向遍历
        for i in range(start, len(candidates)):
            if i > start and candidates[i] == candidates[i-1]: # 去重
                continue
            val = candidates[i]
            if total + val > target: # 剪枝
                break
            path.append(val)
            total += val
            self.tracebacking(candidates, target, total, i+1, path, res) # 纵向递归
            total -= val
            path.pop()

131.分割回文串

class Solution:
    def partition(self, s: str) -> List[List[str]]:
        res = []
        self.tracebacking(s, 0, [], res)
        return res

    def tracebacking(self, s, start, path, res):
        if start == len(s):
            res.append(path[:])

        for i in range(start, len(s)):
            if self.isPalindrome(s, start, i):
                path.append(s[start:i+1])
                self.tracebacking(s, i+1, path, res)
                path.pop()

    def isPalindrome(self, s, start, end):
        while start < end:
            if s[start] != s[end]:
                return False
            start += 1
            end -= 1
        return True