43.字符串相乘.cpp

/*
 * @lc app=leetcode.cn id=43 lang=cpp
 *
 * [43] 字符串相乘
 */

// @lc code=start
class Solution {
public:
    string multiply(string num1, string num2) {
        vector<int> A, B;
        int n = num1.size(), m = num2.size();

        for (int i = n - 1; i >= 0; i--) A.push_back(num1[i] - '0');
        for (int i = m - 1; i >= 0; i--) B.push_back(num2[i] - '0');

        // 不进位乘法
        vector<int> C(n + m);
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                C[i + j] += A[i] * B[j];
            }
        }

        // 处理进位
        for (int i = 0, t = 0; i < C.size(); i++) {
            t += C[i];
            C[i] = t % 10;
            t /= 10;
        }

        // 去 0
        int k = C.size() - 1;
        while (k > 0 && !C[k]) k--;

        // 转为字符串
        string res;
        while (k >= 0) res += C[k--] + '0';

        return res;
    }
};
// @lc code=end