LeetCode-415-String addition

title

Title description: Given two non-negative integers num1 and num2 in the form of strings, calculate their sum.

prompt:

• The length of num1 and num2 are both less than 5100
• Both num1 and num2 only contain numbers 0-9
• Neither num1 nor num2 contains any leading zeros
• You cannot use any built-in BigInteger library, nor can you directly convert the input string to integer form

Please refer to LeetCode official website for example description.

Source: LeetCode
Link: https://leetcode-cn.com/problems/add-strings/
The copyright belongs to Lingkou Network. For commercial reprints, please contact the official authorization. For non-commercial reprints, please indicate the source.

Solution 1: Traverse the string

First, a statement string Result last return value, it is declared I initial value 0, addone to carry the initial value is 0, firstNum and secondNum respectively num1 and num2 current index bit, and then start to traverse the num1 and num2 , the processing process is as follows:

• If i does not exceed the num1 and num2 length, respectively the num1 and num2 assignment numbers current index to firstNum and secondNum , otherwise firstNum and secondNum assignment Is 0;
• Then calculate firstNum + secondNum + addOne result is sum ;
• If sum greater than 9, carry is required, addOne is reset to 1, and sum-10 added to the front of the string of result
• If sum less than 9, there is no need to carry, addOne is reset to 0, and sum added to the front of the string of result
• i plus 1.

Finally, it is judged that addOne is 1, then addOne added to the front of result

Finally, return the result of string addition.

/**
 * @Author: ck
 * @Date: 2021/9/29 8:34 下午
 */
public class LeetCode_415 {
    public static String addStrings(String num1, String num2) {
        String result = "";
        // addOne为进位
        int i = 0, addOne = 0, firstNum = 0, secondNum = 0;
        while (i < num1.length() || i < num2.length()) {
            if (i < num1.length()) {
                // num1中当前位的数字
                firstNum = num1.charAt(num1.length() - 1 - i) - '0';
            } else {
                firstNum = 0;
            }
            if (i < num2.length()) {
                // num2中当前位的数字
                secondNum = num2.charAt(num2.length() - 1 - i) - '0';
            } else {
                secondNum = 0;
            }
            int sum = firstNum + secondNum + addOne;
            if (sum > 9) {
                result = (sum - 10) + result;
                addOne = 1;
            } else {
                result = sum + result;
                addOne = 0;
            }
            i++;
        }
        if (addOne == 1) {
            result = 1 + result;
        }
        return result;
    }


    public static void main(String[] args) {
        // 期望输出: 533
        System.out.println(addStrings("456", "77"));
    }
}

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