Solution Backtracking 1

combination-sum.py

@@ -0,0 +1,32 @@
+# Time Complexity: O(2^(m+n)) 
+# Space Complexity: O(m+n) 
+# Did this code successfully run on Leetcode : Yes
+
+class Solution(object):
+    def combinationSum(self, candidates, target):
+        """
+        :type candidates: List[int]
+        :type target: int
+        :rtype: List[List[int]]
+        """
+        res=[]
+        path=[]
+
+        def helper(pending_target,i,path):
+            #base            
+            if pending_target<0 or i==len(candidates):
+                return
+
+            if pending_target==0:
+                res.append(list(path))
+                return
+
+            #logic
+            helper(pending_target,i+1,path)
+
+            path.append(candidates[i])
+            helper(pending_target-candidates[i],i,path)
+            path.pop()
+
+        helper(target,0,path)
+        return res

expression-add-operators.py

@@ -0,0 +1,57 @@
+
+# Time Complexity: O(4^N) 
+# Space Complexity: O(N) 
+# Did this code successfully run on Leetcode : Yes
+
+class Solution(object):
+    def addOperators(self, num, target):
+        """
+        :type num: str
+        :type target: int
+        :rtype: List[str]
+        """
+        res=[]
+        N=len(num)
+        path=[]
+        def helper(pivot,calc,tail):
+            #base
+            if pivot==N:
+                if calc==target:
+                    res.append(''.join(path))
+                return
+            #logic
+
+            for i in range(pivot,N):
+                if num[pivot]=='0' and pivot!=i:
+                    break
+
+                curr=int(num[pivot:i+1])
+                if pivot==0:
+                    path.append(str(curr))
+                    helper(i+1,curr,curr)
+                    path.pop()
+                    # path.pop()
+                else:
+                    #+
+                    path.append('+')
+                    path.append(str(curr))
+                    helper(i+1,calc+curr,curr)
+                    path.pop()
+                    path.pop()
+
+                    #-
+                    path.append('-')                    
+                    path.append(str(curr))
+                    helper(i+1,calc-curr,-curr)
+                    path.pop()
+                    path.pop()
+
+                    #*
+                    path.append('*')
+                    path.append(str(curr))
+                    helper(i+1,calc-tail+tail*curr,tail*curr)
+                    path.pop()
+                    path.pop()
+
+        helper(0,0,0)
+        return res