Merge pull request #4 from FreeTymeKiyan/Dawei

Create 039_Combination_Sum.cpp

Author: forest5013

039_Combination_Sum.cpp

@@ -0,0 +1,53 @@
+/*
+* Given a set of candidate numbers (C) and a target number (T), find all unique
+* combinations in C where the candidate numbers sums to T.
+
+* The same repeated number may be chosen from C unlimited number of times.
+
+* Note:
+*   All numbers (including target) will be positive integers.
+*  Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
+*  The solution set must not contain duplicate combinations.
+*  For example, given candidate set 2,3,6,7 and target 7, 
+*  A solution set is: 
+*  [7] 
+*  [2, 2, 3] 
+
+ */
+
+#include <vector>
+#include <algorithm>
+using namespace std;
+
+class Solution {
+public:
+    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
+        // sort the candidate vector in ascending order;
+        sort( candidates.begin(), candidates.end() );
+        vector<vector<int> > results;
+        vector<int> combination;
+        sumIteration( candidates, target, results, combination, 0 );
+        return results;
+    }
+    
+private:
+    void sumIteration( vector<int>& candidates, int target, vector<vector<int> >& results, vector<int>&combination, int begin )
+    {
+        if( !target )
+        {
+            results.push_back( combination );
+            return;
+        }
+        for( int i = begin; i< candidates.size() && target >= candidates[i]; i++ )
+        {
+            combination.push_back( candidates[i] );
+            sumIteration( candidates, target - candidates[i], results, combination, i );
+            combination.pop_back();
+        }
+    }
+};
+
+int main( int argc, char ** argv )
+{
+    return 0;
+}