039 Combination Sum py3.py

#!/usr/bin/python3
"""
Given a set of candidate numbers (candidates) (without duplicates) and a target
number (target), find all unique combinations in candidates where the candidate
numbers sums to target.

The same repeated number may be chosen from candidates unlimited number of
times.

Note:

All numbers (including target) will be positive integers.
The solution set must not contain duplicate combinations.
Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
  [7],
  [2,2,3]
]
Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]
"""
from typing import List


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

    def dfs(self, candidates, i, cur, cur_sum, target, ret):
        if cur_sum == target:
            ret.append(list(cur))
            return
            
        if cur_sum > target or i >= len(candidates):
            return

        # not choose A_i
        self.dfs(candidates, i + 1, cur, cur_sum, target, ret)

        # choose A_i
        cur.append(candidates[i])
        cur_sum += candidates[i]
        self.dfs(candidates, i, cur, cur_sum, target, ret)
        cur.pop()
        cur_sum -= candidates[i]