40-Combination-Sum-II.py

'''Leetcode- 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]
]
'''


def combinationSum2(candidates, target):
    candidates.sort()
    res = []

    def backtrack(cur, pos, target):
        if target == 0:
            res.append(cur.copy())
        if target <= 0:
            return
        prev = -1
        for i in range(pos, len(candidates)):
            if candidates[i] == prev:
                continue
            cur.append(candidates[i])
            backtrack(cur, i+1, target-candidates[i])
            cur.pop()
            prev = candidates[i]

    backtrack([], 0, target)
    return res

#T:O(2^n)
#S:O(n)