leetcode 39 Combination Sum

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] 

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class Solution {public:void findNum(vector<int> &candidates, vector<int> container, int target, int i, int sum, vector<vector<int> > &ans) {int n = candidates.size();if(sum == target) {ans.push_back(container);return;}if(i >= n || sum > target || sum+candidates[i]>target) {return;}int cnt = (target-sum)/candidates[i];for(int j = 0; j <= cnt; j++) {for(int k=0; k < j; k++) {container.push_back(candidates[i]);}findNum(candidates, container, target, i+1, sum+candidates[i]*j, ans);for(int k = 0; k < j; k++) {container.erase(container.end()-1);}}}vector<vector<int> > combinationSum(vector<int> &candidates, int target) {vector<int> container;vector<vector<int> > ans;sort(candidates.begin(), candidates.end());findNum(candidates, container, target, 0, 0, ans);reverse(ans.begin(), ans.end());return ans;}}