leetcode——39. 组合总和

思路——回溯

1. 确定递归参数，返回值
2. 确定递归终止条件
3. 确定单层搜索逻辑
4. 数组排序，剪枝，加快搜索

代码

class Solution {
private:
    vector<vector<int>> result;
    vector<int> path;
    void backtracking(vector<int>& candidates, int target, int startIndex){
    	//递归终止条件
        if (target==0) {
            result.push_back(path);
            return;
        }

        // target-candidates[i] >= 0 就终止遍历
        for (int i = startIndex; i < candidates.size() && target-candidates[i] >= 0; i++) {
            path.push_back(candidates[i]);
            backtracking(candidates, target-candidates[i], i);
            path.pop_back();

        }
    }
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        sort(candidates.begin(), candidates.end()); // 需要排序
        backtracking(candidates, target, 0);
        return result;
    }
};