Big integer multiplication python3 implementation

Since python has an infinite int type, it is meaningless to use python to implement the big integer multiplication, but the idea is the same. The law of exploits is that the first I-bit of the first number is multiplied by the second j-bit of the second number, and must be accumulated to the I + j-bit of the result, it starts from 0. The Code is as follows:

Import sysdef list2str (li): while li [0] = 0: del li [0] res = ''for I in li: res + = str (I) return resdef multi (stra, strb): aa = list (stra) bb = list (strb) lena = len (stra) lenb = len (strb) result = [0 for I in range (lena + lenb)] for I in range (lena): for j in range (lenb ): result [lena-i-1 + lenb-j-1] + = int (aa [I]) * int (bb [j]) for I in range (len (result)-1 ): if result [I]> = 10: result [I + 1] + = result [I] // 10 result [I] = result [I] % 10 return list2str (Result [:-1]) if _ name __= = '_ main _': if len (sys. argv )! = 3: print ('enter two parameters') exit () a = sys. argv [1] B = sys. argv [2] res = multi (a, B) print ('multi ', res) print (' OK ', int (a) * int (B ))

The multi function is the main function for multiplying large integers. The input is two large integers in the string format, and the output is the result of the string format; the list2str function converts the list containing each digit to str, and deletes the 0 value of the highest placeholder. The output result is as follows:

After multi, the result is calculated using a general big integer. After OK, the result is a multiplication result directly calculated by python itself for comparison.

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