415. Add Strings
BitInteger的最简单的部分
把两个string反过来,从后往前加,可以学习的地方是对于while的条件可以设置成,index1< len1 || index2 < len2.
然后在内部分别对index1 < len1和index2 <len2处理,这样就不用对其中一个提前结束的情况单独再写一个循环了
1 public String addStrings(String num1, String num2) { 2 if(num1 == null) { 3 return num2; 4 } 5 if(num2 == null) { 6 return num1; 7 } 8 StringBuilder sb1 = new StringBuilder(num1); 9 StringBuilder sb2 = new StringBuilder(num2); 10 int len1 = num1.length(); 11 int len2 = num2.length(); 12 sb1.reverse(); 13 sb2.reverse(); 14 StringBuilder sb = new StringBuilder(); 15 int index1 = 0; 16 int index2 = 0; 17 int carry = 0; 18 while(index1 < len1 || index2 < len2) { 19 int cur = carry; 20 if(index1 < len1) { 21 cur += sb1.charAt(index1++) - '0'; 22 } 23 if(index2 < len2) { 24 cur += sb2.charAt(index2++) - '0'; 25 } 26 if(cur > 9) { 27 cur %= 10; 28 carry = 1; 29 } else { 30 carry = 0; 31 } 32 sb.append(cur); 33 } 34 if(carry == 1) { 35 sb.append(1); 36 } 37 return sb.reverse().toString(); 38 }