AddStrings [source code]

public class AddStrings {
    public String addStrings(String num1, String num2) {
        char[] digits1 = num1.toCharArray(), digits2 = num2.toCharArray();
        int len1 = num1.length(), len2 = num2.length();
        int len = Math.max(len1, len2);
        if (len == 0) return "";
        int carry = 0;
        String res = "";
        for (int i = 0; i < len; i++) {
            int index1 = len1 - 1 - i;
            int index2 = len2 - 1 - i;
            int digit1 = index1 >= 0 ? digits1[index1] - '0' : 0;
            int digit2 = index2 >= 0 ? digits2[index2] - '0' : 0;
            int sum = digit1 + digit2 + carry;
            carry = sum / 10;
            res = (sum % 10) + res;
        }
        return carry == 1 ? "1" + res : res;
    }

    public static void main(String[] args) {
        AddStrings tester = new AddStrings();
        System.out.println(tester.addStrings("123", "932"));
    }
}

总体的思路是很简单, 就是按 bit 扫描; 一个小技巧就是loop var应该用从0开始, 然后里面再用 index 转换. 因为 len 本身是 len1和 len2的最大值, 所以从0开始向上增长, 在分段函数的分段逻辑的区分上更好处理一些.

这里要注意的是Integer.parseInt这个这里不好用, 不能用在 char 上. 直接用类似字母的方法来处理, 一个减法就行了.

最后的速度倒是很差, 不知道为什么: 70(10).

Problem Description

Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

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.
Difficulty:Easy
Category:Algorithms
Acceptance:41.24%
Contributor: LeetCode
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Related Topics
math
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