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Author: assassint2017

Combinations/Combinations.cpp

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+// 典型的回溯法
+
+// Runtime: 84 ms, faster than 66.79% of C++ online submissions for Combinations.
+// Memory Usage: 11.8 MB, less than 66.84% of C++ online submissions for Combinations.
+
+class Solution 
+{
+public:
+    vector<vector<int>> combine(int n, int k) 
+    {
+        // 边界条件处理
+        if (k <= 0 || n <= 0 || k > n)
+            return vector<vector<int>>();
+        
+        vector<int> candidate(n, 0);
+        for (int i = 0; i < n; ++i)
+            candidate[i] = i + 1;
+        
+        vector<vector<int>> res;
+        vector<int> temp;
+        
+        helper(res, candidate, temp, 0, k);
+        return res;
+    }
+private:
+    void helper(vector<vector<int>>& res, vector<int>& candidate, vector<int>& temp, int start, int k)
+    {
+        if (temp.size() == k)
+        {
+            res.push_back(temp);
+            return ;
+        }
+        for (int i = start; i < candidate.size(); ++i)
+        {
+            temp.push_back(candidate[i]);
+            helper(res, candidate, temp, i + 1, k);
+            temp.pop_back();
+        }
+    }
+};