【LeetCode 415】 Add Strings

题目描述

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.

代码

class Solution {
public:
    string addStrings(string num1, string num2) {
        int n1 = num1.length();
        int n2 = num2.length();
        int cnt = max(n1, n2);
        string ans(cnt+1, '0');
        int p = cnt;
        int p1 = n1-1, p2 = n2-1;
        int jin = 0;
        while(p1>=0 || p2>=0) {
            int tmp1 = 0, tmp2 = 0;
            if (p1 >= 0) tmp1 = num1[p1] - '0';
            if (p2 >= 0) tmp2 = num2[p2] - '0';
            int cur = tmp1 + tmp2 + ans[p] - '0';
            if (cur >= 10) jin = 1;
            else jin = 0;
            ans[p-1] = jin + '0';
            cur = cur % 10;
            ans[p] = cur + '0';
            p--;
            p1--;
            p2--;
        }
        if (p != -1) {
            int pos = p;
            if (ans[p] != '0') pos--;
            ans.erase(0, pos+1);
        }
        return ans;
    }
};