Leetcode: Add Strings

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Add 2 strings of big numbers

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Similar Problems:

• LeetCode: Add to Array-Form of Integer
• LintCode: K Decimal Addition
• Additive Number

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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.

• Both num1 and num2 contains only digits 0-9.
• Both num1 and num2 does not contain any leading zero.
• You must not use any built-in BigInteger library or convert the inputs to integer directly.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

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// https://code.dennyzhang.com/add-strings
// Basic Ideas: 
//  Handle carry
//  Only stop when both strings have finished
// Complexity: Time O(n), Space O(n)
import "strconv"
func addStrings(num1 string, num2 string) string {
    carry, res := 0, ""
    for i, j:= len(num1)-1, len(num2)-1;
        i>=0 || j>=0 || carry!=0; 
        i, j = i-1, j-1 {
        v1, v2, v := 0, 0, 0
        if i>=0 { v1, _ = strconv.Atoi(string(num1[i])) }
        if j>=0 { v2, _ = strconv.Atoi(string(num2[j])) }
        v = v1+v2+carry
        if v>=10 {
            carry = 1
            v -= 10
        } else {
            carry = 0
        }
        res = strconv.Itoa(v)+res
    }
    return res
}