LeetCode 39. Combination Sum

题目

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]
]

思路

首先把数组sort一遍,这样如果处理边界问题比较省时(比如sum已经大于target, 则没有必要继续了)

Swift 题解

func combinationSum(_ candidates: [Int], _ target: Int) -> [[Int]] {  
        var result = [[Int]]()

        var current = [Int]()

        let sorted = candidates.sorted()

        dfs(result: &result, current: &current, target: target, level: 0, candidates: sorted)


        return result

    }

    func dfs(result: inout [[Int]], current: inout [Int], target: Int, level: Int, candidates: [Int]) {
        if target == 0 {
            result.append(current)
            return
        }

        if target < 0 {
            return
        }

        for i in level..<candidates.count {
            current.append(candidates[i])
            dfs(result: &result, current: &current, target: target - candidates[i], level: i, candidates: candidates)
            current.removeLast()
        }
    }

chenbo

编程爱好者

Singapore