leetcode 415 Add Strings
z
 2019-04-11 12:15:29  

Given two non-negative integers num1and 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.
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class Solution {
    public String addStrings(String num1, String num2) {
        int i=num1.length()-1;
        int j=num2.length()-1;
        int carry = 0;
        StringBuilder ans = new StringBuilder();
        while (i>=0 || j>=0) {
            int a = i>=0? num1.charAt(i)-'0': 0;
            int b = j>=0? num2.charAt(j)-'0': 0;
            int sum = (a+b+carry)%10;
            carry = (a+b+carry)/10;
            ans.insert(0, sum);
            j--;
            i--;
        }
        if (carry != 0)
            ans.insert(0, carry);
        return ans.toString();
    }
}