sum of lists

Author: saarikabhasi

cracking-the-coding-interview-problems/linkedlist/sum-of-lists.py

@@ -0,0 +1,259 @@
+"""
+Cracking the coding interview 
+page #95, question #2.5
+
+You have two numbers represented by a linked list, where each node contains a single digit. 
+The digits are stored in reverse order, such that the 1's digit is at the head of the list. 
+Write a function that  adds the two numbers and returns the sum as a linked list.
+
+Example:
+7->1->6 + 5->9->2  That is 617+295 = 912
+head of list 1 is 7
+head of list 2 is 5
+
+Follow up 
+
+Suppose the digits are stored in forward order. Repeat the above problem. 
+6->1->7 + 2->9->5  That is 617+295 = 912
+
+head of list 1 is 6
+head of list 2 is 2
+
+"""
+class Stack():
+    def __init__(self) -> None:
+        self.s = [None]*6
+        self.top = None
+
+    def push(self,data):
+        if self.top == None :
+            self.top = 0
+            self.s[self.top] = data
+        else:
+            self.top +=1
+            self.s[self.top ] =data
+
+    def pop(self):
+        if self.top == -1:
+            print("stack empty")
+            self.top = None
+        else:
+            t = self.s[self.top]
+            # self.s.pop(self.top)
+            del self.s[self.top]
+            self.top -=1
+        return t
+    def show(self):
+        p = self.top
+        while p !=None:
+            print(self.s[p])
+            p -=1
+        print("============")
+        
+
+class Node():
+    def __init__(self,data) -> None:
+        self.data = data
+        self.next = None
+
+class singlelinkedlist():
+    def __init__(self) -> None:
+        self.head = None
+    
+    def insert(self,data):
+        """
+        insert the data to the linked list
+        """
+        node = Node(data)
+        if self.head is None:
+            self.head = node
+        else:
+            p=self.head
+            while p.next:
+                p = p.next
+            p.next =node
+        
+    def show(self):
+        print("------------------------")
+        p =self.head
+        if p:
+            while p:
+                print(p.data)
+                p = p.next
+
+        else:
+            print("List empty")
+        print("------------------------")
+
+class addDigits():
+    def __init__(self,lobj1,lobj2) -> None:
+        # self.result = super().__init__()
+        self.d1 = lobj1
+        self.d2 = lobj2
+        
+
+    def addDigitsinreverse(self):
+        """
+        Add the digits stored in reverse order, Meaning head points to unit digit
+        return other list if any of the list is empty
+
+        """
+
+        if self.d1.head == None:
+            return self.d2
+        elif self.d2.head == None:
+            return self.d1
+        else:
+            p1 =self.d1.head
+            p2 =self.d2.head
+            carry =0 
+            self.result = singlelinkedlist()
+            while p1 !=None or p2!=None:
+                if p1 and p2:
+                    r = p1.data + p2.data +carry
+                    p1 = p1.next
+                    p2 = p2.next
+                elif p1:
+                    r = p1.data+carry
+                    p1 = p1.next
+                else:
+                    r = p2.data+carry
+                    p2 = p2.next
+
+                carry = 0
+                if r>=10:
+                    self.result.insert(r%10)
+                    carry = r //10
+                else:
+                    self.result.insert(r)
+            
+            if carry >0:
+                self.result.insert(carry)
+                
+                
+        return self.result
+                
+    def addDigitsinforward_withstack(self):
+        """
+        Add the digits stored in list in forward order. Meaning head points to last place of digit
+        
+        """
+        if not self.d1.head:
+            return self.d2
+        elif not self.d2.head:
+            return self.d1
+        else:
+            
+            p1 = self.d1.head
+            p2 = self.d2.head
+            
+            stack = Stack()
+            result = singlelinkedlist()
+            
+            s1 = self.d1.head 
+            s2 = self.d2.head
+
+            size1 = 0
+            size2 = 0
+
+            while s1:
+                size1 +=1
+                s1 =s1.next
+
+            while s2:
+                size2 +=1
+                s2 =s2.next
+
+            if size2>size1:
+                pass
+            else:
+                pass
+        
+
+            
+
+            while p1 or p2:
+       
+                if not p1:
+                    stack.push( p2.data)
+                    p2 = p2.next
+                elif not p2:
+                    stack.push( p1.data)
+                    p1 = p1.next
+                else:
+                    stack.push(p1.data + p2.data)
+                    p1 = p1.next
+                    p2 = p2.next
+
+                
+            
+            carry = 0 
+            while stack.top>=0:
+                add = stack.pop()
+                
+                node = Node(add%10+carry)
+                if add >=9:
+                    
+                    if result.head == None:
+                        # 
+                        result.head = node
+                        
+                    
+                    else:
+                        node.next = result.head
+                        result.head = node
+
+                    carry = 1
+                        
+                        
+                else:
+                    if result.head == None:
+
+                        result.head = node
+                    else:
+                        node.next = result.head 
+                        result.head = node
+                        carry = 0
+                
+        return result
+
+
+                    
+                
+            
+            
+
+# lobj1 = singlelinkedlist()
+# lobj1.insert(8)
+# lobj1.insert(9)
+# lobj1.show()
+
+# lobj2 = singlelinkedlist()
+# lobj2.insert(2)
+# lobj2.insert(0)
+# lobj2.insert(1)
+
+# lobj2.show()
+
+# aobj1  = addDigits(lobj1,lobj2)
+# res1 = aobj1.addDigitsinreverse()
+# print("Result")
+# res1.show()
+
+#example2 forward
+lobj3 = singlelinkedlist()
+# lobj3.insert(6)
+lobj3.insert(1)
+lobj3.insert(7)
+
+lobj4 = singlelinkedlist()
+lobj4.insert(2)
+lobj4.insert(9)
+lobj4.insert(5)
+
+aobj2  = addDigits(lobj3,lobj4)
+res2 = aobj2.addDigitsinforward_withstack()
+print("Result")
+res2.show()
+
+