Combination Sum II

Problem

https://leetcode.com/problems/combination-sum-ii/

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to target.

Each number in candidates may only be used once in the combination.

Note: The solution set must not contain duplicate combinations.

Example 1:

Input: candidates = [10,1,2,7,6,1,5], target = 8
Output:
[
[1,1,6],
[1,2,5],
[1,7],
[2,6]
]

Example 2:

Input: candidates = [2,5,2,1,2], target = 5
Output:
[
[1,2,2],
[5]
]

Constraints:

  • 1 <= candidates.length <= 100

  • 1 <= candidates[i] <= 50

  • 1 <= target <= 30

Pattern

Array, Backtracking

Approaches

Code

def combinationSum2(candidates: list[int], target: int) -> list[list[int]]:
    result = []

    candidates = sorted(candidates)

    def combination_sum(combination, i):
        s = sum(combination)

        if s == target:
            result.append(combination.copy())
            return

        if s > target:
            return

        if i >= len(candidates):
            return

        for j in range(i, len(candidates)):
            if s + candidates[j] > target:
                break

            if j > i and candidates[j] == candidates[j - 1]:
                continue

            combination_sum(combination + [candidates[j]], j + 1)

    combination_sum([], 0)
    return result

Test

>>> from combination_sum_ii__backtracking import combinationSum2
>>> sorted([sorted(c) for c in combinationSum2([10, 1, 2, 7, 6, 1, 5], 8)])
[[1, 1, 6], [1, 2, 5], [1, 7], [2, 6]]
>>> sorted([sorted(c) for c in combinationSum2([2, 5, 2, 1, 2], 5)])
[[1, 2, 2], [5]]
combination_sum_ii__backtracking.combinationSum2(candidates: list[int], target: int) → list[list[int]]