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combination_sum.cpp
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combination_sum.cpp
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class Solution {
public:
void backtracking(vector<vector<int>>& res, vector<int>& candidates, vector<int>& tmp, int target, int index){
int sum = 0;
for (int i=0; i<tmp.size(); i++)
sum += tmp[i];
if (sum == target){
res.push_back(tmp);
}
if (sum < target){
for (int i=index; i<candidates.size(); i++){ //从index开始添加元素
tmp.push_back(candidates[i]);
backtracking(res, candidates, tmp, target, i);
tmp.pop_back();
}
}
}
vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
sort(candidates.begin(), candidates.end());
vector<vector<int>> res;
vector<int> tmp;
backtracking(res, candidates, tmp, target, 0);
return res;
}
};
//方法:
// 逐个添加元素,验证已选元素的和sum是否有sum==target
// 如果sum<target 说明还可以添加元素(用递归添加)
// 如果sum==target 说明当前已添加的元素符合条件,纳入结果res中
// 注意:先给candidates排序