306. Additive Number

Additive number is a string whose digits can form Additive sequence.

A valid additive sequence should contain at least three numbers. Except for the first and numbers, each subsequent number in the sequence must is the sum of the preceding.

For example:
"112358"is a additive number because the digits can form an additive sequence: 1, 1, 2, 3, 5, 8 .

1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8

"199100199"is also a additive number, the additive sequence is: 1, 99, 100, 199.

1 + 99 = 100, 99 + 100 = 199

Note:numbers in the additive sequence cannot has leading zeros, so sequence 1, 2, 03 or is 1, 02, 3 invalid.

Given a string containing only digits ‘0‘-‘9‘ , write a function to determine if it's an additive number.

Follow up:
How would handle overflow for very large input integers?

 Public classSolution { Public Booleanisadditivenumber (String num) {intL =num.length (); if(l<3)            return false; if(Num.startswith ("00"))//Then the whole string should is "..."        {             for(inti=2;i<l;++i) {if(Num.charat (i)! = ' 0 ')                    return false; }            return true; }                intFirstnumendindex = (L-1)/2; if(Num.startswith ("0"))//Then 0 must is the first Interger.Firstnumendindex = 1;  for(inti = 1; I<= Firstnumendindex; ++i) {String add1= num.substring (0, I);//[0, i) + = First number             for(intj = i+1; j<= L-math.max (i,j-i); ++j) {String add2= Num.substring (i, j);//[I, j] = = Second number                if(Add2.equals ("0"))                {                    if(Rolltoend (num, Add1, ADD2, j))return true;  Break; }                    if(Rolltoend (num, Add1, ADD2, j))return true; }        }        return false; }            //[Start,end]    Private BooleanRolltoend (String num, String add1, String add2,intFrom ) {String sumstring=getsumstring (ADD1, ADD2); String Rest=num.substring (from); if(Rest.startswith ("0"))            return false; if(Rest.equals (sumstring))return true; if(Rest.startswith (sumstring))returnRolltoend (num, add2, sumstring, from+sumstring.length ()); return false; }        Privatestring getsumstring (String add1, String add2) {intExtra = 0; intL1 =add1.length (); intL2 =add2.length (); Deque<Integer> sum =NewArraydeque<integer>();  while(L1>0 && l2>0)        {            intA1 = Add1.charat (l1-1)-' 0 '; intA2 = Add2.charat (l2-1)-' 0 '; ints = a1+a2+Extra; Extra= S/10; Sum.push (S%10); --L1; --L2; }                 while(l1>0)        {            intA = Add1.charat (l1-1)-' 0 '; ints = A +Extra; Extra= S/10; Sum.push (S%10); --L1; }                 while(l2>0)        {            intA = Add2.charat (l2-1)-' 0 '; ints = A +Extra; Extra= S/10; Sum.push (S%10); --L2; }                if(Extra = = 1) Sum.push (extra); StringBuilder SB=NewStringBuilder ();  while(!sum.isempty ()) Sb.append (Sum.pop ()); returnsb.tostring (); }}

306. Additive number