Completed Backtracking-1

combination_sum_282.cpp

@@ -0,0 +1,34 @@
+class Solution {
+public:
+  vector<vector<int>> result;
+    //vector<vector<int>> result;
+    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
+      if(candidates.size()==0)
+        return {};
+    vector<int> path;
+
+    recurse(candidates,target,0 ,path);
+    return result;  
+    }
+    void recurse(vector<int>& candidates, int target, int index, vector<int>&path)
+    {
+        //base
+        if(target==0)
+        {
+            result.push_back(path);
+        }   
+        if(target<0)
+        {
+            return;
+        }
+
+        //logic
+        for(int i=index;i<candidates.size();i++)
+        {
+            path.push_back(candidates[i]);
+            recurse(candidates, target-candidates[i], i, path);
+            path.pop_back();
+        }
+
+    }
+    };

expressionAdd_operator_39.cpp

@@ -0,0 +1,54 @@
+//TC: O(n*4^n)
+//SC:
+class Solution {
+public:
+vector<string> res;
+    vector<string> addOperators(string num, int target) {
+        if(num.empty())
+            return {};
+        string expression="";
+        recurse(num, target, 0, 0, 0, expression);
+
+    return res;
+    }
+    void recurse(string num, int target, int index, long calc, long tail, string exp)
+    {   
+        //base
+        if(index==num.size()) //at the end of string 
+        {
+             if(target==calc) 
+            {
+                res.push_back(exp);
+                return;
+            }
+        }
+
+
+        ///logic
+        string currString="";
+        long long currNum=0;
+        for(int i=index; i<num.size();++i)
+        {
+            if(i>index && num[index]=='0')break;
+
+            currString+=num[i];
+            currNum=currNum*10+(num[i]-'0');
+
+            if(index==0)
+            { 
+                recurse(num, target, i+1, calc+currNum, currNum, exp+currString);
+            }
+            else
+            {
+            //+
+            recurse(num, target, i+1, calc+currNum,+currNum, exp+"+"+currString);
+            //-
+            recurse(num, target, i+1, calc-currNum, -currNum, exp+"-"+currString);
+            //*
+            recurse(num, target, i+1, calc-tail+tail*currNum, tail*currNum, exp+"*"+currString);
+            }
+
+        }
+
+    }
+};