int n1 = num1.length(), n2 = num2.length();
int i = n1-1, j = n2-1, one = 0, bit1, bit2...0 : (num1[i]-'0');//位数不够了,前面补0
bit2 = j<0 ?...int n1 = num1.length(), n2 = num2.length();
int i = n1-1, j = n2-1, one = 0, bit1, bit2...0 : (num1[i]-'0');
bit2 = j<0 ?