Combination Sum
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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]
class Solution { public: int _sum(vector<int> tmp) { int sum = 0; int i; for (i=0; i<tmp.size(); i++){ sum+= tmp[i]; } return sum; } void combination(vector<int>& candidates, vector<vector<int>> &res, vector<int> tmp, int target, int start) { //计算选择集的和 int sum = _sum(tmp); if (start >= candidates.size() || sum > target || sum + candidates[start] > target) { return; } //计算该选择集是否可以包含当前数,包含多少个 int num_add = (target - sum) / candidates[start]; int num_mod = (target - sum) % candidates[start]; int i = 0; //循环num_add次,每次增加一个当前数到选择集中,然后将当前数设置为下一个,进行计算 while (i < num_add) { i++; sum += candidates[start]; tmp.push_back(candidates[start]); //避免函数调用浪费时间 if (start < candidates.size() -1) { combination(candidates, res, tmp, target, start + 1); } } //如果当前选择集合的和正好等于target,加入结果集 if (num_add && i == num_add && !num_mod) { res.push_back(tmp); } //将选择集合中所有的当前数去掉,然后计算不包含当前数时 while (i--) { tmp.pop_back(); } combination(candidates, res, tmp, target, start + 1); } vector<vector<int>> combinationSum(vector<int>& candidates, int target) { vector<int> tmp = {}; int start = 0; vector<vector<int>> res; sort(candidates.begin(), candidates.end()); combination(candidates, res, tmp, target, start); return res; } };
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