Done Backtracking 1

Problem1.py

@@ -0,0 +1,33 @@
+#39. Combination Sum
+
+from typing import List
+
+
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        self.result=[]
+
+        self.helper(0, candidates, target, [])
+        return self.result
+
+
+    def helper(self, index, candidates, target, potentialCand):
+
+        if target==0:
+            self.result.append(potentialCand[:])
+            return
+
+        if index == len(candidates) or target<0:
+            return
+
+
+        #no choose:
+        self.helper(index+1, candidates, target, potentialCand)
+
+        #choose candidate
+        potentialCand.append(candidates[index])
+        self.helper(index, candidates, target-candidates[index], potentialCand)
+        potentialCand.pop()
+
+sol = Solution()
+print(sol.combinationSum([2], 1))

Problem2.py

@@ -0,0 +1,48 @@
+# time complexity 4^n since we have 4 sub recursion paths at every number
+# spac complexity -> On as we are saving only the digits in the pathlist array 
+# logic -> using pivot and i create the possible combinations of numbers and between every 2 numbers try all 3 operations
+
+class Solution:
+    def addOperators(self, num: str, target: int) -> List[str]:
+        result = []
+        digits = [int(d) for d in num]
+        def helper(pivot, pathList, calc, tail):
+            if pivot == len(num):
+                if calc == target:
+                    result.append("".join(pathList))
+            curr = 0
+            for i in range(pivot, len(num)):
+                if digits[pivot] == 0 and pivot != i:
+                    break
+                curr = curr*10 + digits[i]
+                currStrNum = num[pivot:i+1]
+                if pivot == 0:
+                    pathList.append(currStrNum)
+                    helper(i+1, pathList, curr, curr)
+                    pathList.pop()
+                else:
+                    #addition
+                    pathList.append("+")
+                    pathList.append(currStrNum)
+                    helper(i+1, pathList, calc+curr, curr)
+                    pathList.pop()
+                    pathList.pop()
+
+
+                    #subtraction
+                    pathList.append("-")
+                    pathList.append(currStrNum)
+                    helper(i+1, pathList, calc-curr, -curr)
+                    pathList.pop()
+                    pathList.pop()
+
+
+                    # multiply
+                    pathList.append("*")
+                    pathList.append(currStrNum)
+                    helper(i+1, pathList, calc-tail+(tail*curr), (tail*curr))
+                    pathList.pop()
+                    pathList.pop()
+        helper(0, [], 0, 0,)
+        return result
+