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Author: assassint2017

Combination Sum II/Combination_Sum_II.cpp

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+// 典型的回溯法
+// Runtime: 8 ms, faster than 86.52% of C++ online submissions for Combination Sum II.
+// Memory Usage: 8.8 MB, less than 94.33% of C++ online submissions for Combination Sum II.
+
+class Solution 
+{
+public:
+    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) 
+    {
+        // 边界条件处理
+        sort(candidates.begin(), candidates.end());
+        if (candidates.size() == 0 || candidates[0] > target)
+            return vector<vector<int>>();
+        
+        vector<vector<int>> res;
+        vector<int> temp;
+        
+        helper(res, candidates, temp, target, 0, 0);
+        return res;
+    }
+    
+private:
+    void helper(vector<vector<int>>& res, vector<int>& candidates, vector<int>& temp, int target, int curSum, int start)
+    {
+        if (curSum == target)
+        {
+            res.push_back(temp);
+            return ;
+        }
+        
+        for (int i = start; i < candidates.size(); ++i)    
+        {
+            if (curSum + candidates[i] > target)
+                break;
+            if (i > start && candidates[i] == candidates[i - 1])
+                continue;
+            
+            curSum += candidates[i];
+            temp.push_back(candidates[i]);
+            
+            helper(res, candidates, temp, target, curSum, i + 1);
+            
+            curSum -= candidates[i];
+            temp.pop_back();
+        }
+    }
+};