LeetCode Add Strings

原题链接在这里：https://leetcode.com/problems/add-strings/

题目：

Given two non-negative numbers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

1. The length of both num1 and num2 is < 5100.
2. Both num1 and num2 contains only digits 0-9.
3. Both num1 and num2 does not contain any leading zero.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

题解：

两个string的末位相加放到string builder尾部.

Time Complexity: O(n). n是较长string的length.

Space: O(n).

AC Java:

 public class Solution {
     public String addStrings(String num1, String num2) {
         StringBuilder sb = new StringBuilder();
         int carry = 0;
         int i = num1.length()-1;
         int j = num2.length()-1;
         while(i>=0 || j>=0 || carry!=0){
             carry += (i<0) ? 0 : num1.charAt(i)-'0';
             carry += (j<0) ? 0 : num2.charAt(j)-'0';
             sb.insert(0, carry%10);
             carry /= 10;
             i--;
             j--;
         }
         return sb.toString();
     }
 }

跟上Multiply Strings.

类似Add Two Numbers II, Add Binary, Plus One.