Given two non-negative integers 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.

Solution: Brute Force

Time complexity: O(n)

Space complexity: O(n)

C++

// Author: Huahua
// Running time: 13 ms
class Solution {
public:
  string addStrings(string num1, string num2) {
    if (num1.length() < num2.length()) swap(num1, num2);
    num1 = "0" + num1;
    int l1 = num1.length();
    int l2 = num2.length();
    for (int i = 0; i < l1 - 1; ++i) {
      if (i < l2) num1[l1 - i - 1] += (num2[l2 - i - 1] - '0');
      if (num1[l1 - i - 1] > '9') {
        num1[l1 - i - 1] -= 10;
        ++num1[l1 - i - 2];
      }
    }    
    return (num1[0] != '0') ? num1 : num1.substr(1);
  }
};

The post 花花酱 LeetCode 415. Add Strings appeared first on Huahua's Tech Road.