Plus 1(p-66)

class Solution:
    def plusOne(self, digits: List[int]) -> List[int]:
        #evaluating digits Array by adding 1 to the last elements with O(n) and if all the  elements of the list becomes zero then 1 is append to the list 
        c=0
        i=len(digits)-1
        if(digits[i]+1)<=9:
            digits[i]=digits[i]+1
        else: 
            c=1
            digits[i]=0
            j=i-1
            s=0
            while j>=0:
                if(c>0):
                    s=1+digits[j]
                if s>9:
                    c=1
                    digits[j]=0
                else:
                    c=0
                    digits[j]=s
                    break
                    
                j-=1
        #if there is carry after iteration we insert the carry to the last new element of  the list 
        if c>0:
            digits.append(1)
            f=0
            e=len(digits)-1
        #After that reversing the list will generate the exact answer with time complexity  O(n) and space com. O(1)
            while f<e:
                t1=digits[e]
                t2=digits[f]
                digits[f]=t1
                digits[e]=t2
                f+=1
                e-=1
        
            
        
        return digits