
深度优先搜索(回溯)
class Solution {
public:
vector<vector<int>>ans;
vector<int>path;
vector<vector<int>> combinationSum2(vector<int>& nums, int target) {
sort(nums.begin(),nums.end());
dfs(nums,0,target);
return ans;
}
void dfs(vector<int>&nums,int u,int target){
if(target==0){
ans.push_back(path);
return ;
}
if(u==nums.size())return;
int k=u+1;
while(k<nums.size() && nums[k]==nums[u])k++;
int cnt=k-u;
for(int i=0;nums[u]*i<=target && i<=cnt;i++){
dfs(nums,k,target-nums[u]*i);
path.push_back(nums[u]);
}
for(int i=0;i*nums[u]<=target && i<=cnt;i++){
path.pop_back();
}
}
};