LeetCode:Combination Sum（回溯的经典框架（路径描述））

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, … , a_k) must be in non-descending order. (ie, a₁ ≤ a₂ ≤ … ≤ a_k).
• 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:
    vector<vector<int>> combinationSum(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        vector<vector<int>> result;
        vector<int> path;
        DFS(nums,0,target,path,result);
        return result;    
        
    }
    void DFS(vector<int> &nums,int start,int gap,vector<int> path,vector<vector<int>> &result)
    {   
        //找到一个合法解
        if(gap==0)
        {
            result.push_back(path);
            return;
        }
        
        for(int i=start;i<nums.size();i++)
        {
            //剪枝
            if(gap<nums[i]) return;
            
            path.push_back(nums[i]);  //执行扩展动作
            DFS(nums,i,gap-nums[i],path,result);
            path.pop_back(); //撤销动作
        }
        
    }
};