39. Combination Sum (Back-Track)
Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.
The same repeated number may be chosen from C unlimited number of times.
Note:
- All numbers (including target) will be positive integers.
- Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
- The solution set must not contain duplicate combinations.
For example, given candidate set 2,3,6,7
and target 7
,
A solution set is: [7]
[2, 2, 3]
思路:每个元素有被选和不选两种情况=>带回溯的递归
class Solution { public: vector<vector<int>> combinationSum(vector<int>& candidates, int target) { sort(candidates.begin(), candidates.end()); backTracking(candidates,0,target); return result; } void backTracking(vector<int>& candidates, int depth, int target){ if(target==0){ result.push_back(item); return; } if(target<0 || depth >= candidates.size()) return; item.push_back(candidates[depth] ); backTracking(candidates,depth, target-candidates[depth]); item.pop_back(); backTracking(candidates,depth+1, target); } private: vector<int> item; vector<vector<int>> result; };