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] 

class Solution {
public:
    void visit(vector<int> &candidates, int n, int pos, int target, int sum,  
               vector<vector<int> > &result, vector<int> &buf)
    {
	    if (sum == target)
	    {
		    result.push_back(buf);
		    return;
	    }
	    if (pos >= n)
	    {
		    return;
	    }

	    int i =  0;
	    while (true)
	    {
		    int temp = sum + candidates[pos]*i;
		    if (temp > target)
		    {
			    break;
		    }
		    else
		    {
			    for (int j = 0; j < i; j++)
			    {
				    buf.push_back(candidates[pos]);
			    }
			    visit(candidates, n, pos+1, target, temp, result, buf);
			    for (int j = 0; j < i; j++)
			    {
				    buf.pop_back();
			    }
		    }
		    i++;
	    }
    }

    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        int n = candidates.size();
	    sort(candidates.begin(), candidates.end());

	    vector<vector<int> > result;
	    vector<int> buf;
	    int sum = 0; 
	    visit(candidates, n, 0, target, sum, result, buf);

	    return result;  
    }
};