LeetCode 415: Add Strings Solution

Master LeetCode problem 415 (Add Strings), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

415. Add Strings

Easy

Math String Simulation

Problem Explanation

Explanation:

To add two numbers represented as strings without using any built-in libraries, we can simulate the addition process digit by digit, from right to left. We start by initializing pointers at the end of both strings and then iteratively add the digits, keeping track of the carry. We continue this process until we reach the beginning of both strings.

The key steps of the algorithm:

Initialize two pointers at the end of both input strings.
Traverse both strings from right to left, adding the corresponding digits along with the carry.
Append the result to the beginning of the output string.
Handle any remaining carry after both strings are exhausted.

Time complexity: O(max(n, m)) where n and m are the lengths of the input strings num1 and num2. Space complexity: O(max(n, m)) for storing the result.

Java:

Solution Code

class Solution {
    public String addStrings(String num1, String num2) {
        StringBuilder result = new StringBuilder();
        int carry = 0;
        int i = num1.length() - 1;
        int j = num2.length() - 1;

        while (i >= 0 || j >= 0 || carry > 0) {
            int sum = carry;
            if (i >= 0) {
                sum += num1.charAt(i--) - '0';
            }
            if (j >= 0) {
                sum += num2.charAt(j--) - '0';
            }
            result.insert(0, sum % 10);
            carry = sum / 10;
        }

        return result.toString();
    }
}

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