【Leetcode】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]

先排序，再深搜，深搜过程中要注意防止出现重复的组合。

class Solution {
public:
vector<vector<int> > res;
vector<int> com;

void combineSum(vector<int> &nums, int start, int target)
{
if (target==0)
{
res.push_back(com);
return;
}
if (target<=0 || start>=nums.size()) return;

com.push_back(nums[start]);
combineSum(nums,start,target-nums[start]);
com.pop_back();
// avoid repeated combinations
while(start+1<nums.size() && nums[start]==nums[start+1])
++start;
combineSum(nums,start+1,target);
}
vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
res.clear();
com.clear();
sort(candidates.begin(),candidates.end());
combineSum(candidates,0,target);
return res;
}
};