[笔试强训day06]

#include <string>
#include <vector>
class Solution {
  public:

    string solve(string s, string t) {
        int m = s.size(), n = t.size();
        reverse(s.begin(), s.end());
        reverse(t.begin(), t.end());

        //1.无进位相加并相乘
        vector<int> tmp(m + n);
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                tmp[i + j] += (s[i] - '0') * (t[j] - '0');
            }
        }
        //2.处理进位
        int c = 0;
        string ans;
        for (auto x : tmp) {
            c = c + x;
            ans += c % 10 + '0';
            c = c / 10;
        }
        while (c) {
            ans += c % 10 + '0';
            c /= 10;
        }

        //3.处理前置0
        while (ans.size() > 1 && ans.back() == '0') ans.pop_back();

        reverse(ans.begin(), ans.end());
        return ans;

    }
};

#include <type_traits>
class Solution {
public:

    string solve(string s, string t) {
        int i=s.size()-1,j=t.size()-1;
        int tmp=0;  //进位符
        string ans;
        while(i>=0||j>=0||tmp)
        {
            int sum=0;
            if(i>=0) tmp+=s[i--]-'0';
            if(j>=0) tmp+=t[j--]-'0';
            ans+=tmp%10+'0';
            tmp/=10;
        }
        reverse(ans.begin(),ans.end());
        return ans;
    }
};

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
#include <new>
class Solution {
public:
    ListNode* reverse(ListNode* head)
    {
        ListNode* newhead=new ListNode(0);
        ListNode* cur=head;

        while(cur)
        {
            ListNode* next=cur->next;
            cur->next=newhead->next;
            newhead->next=cur;
            cur=next;
        }
        cur=newhead->next;
        delete newhead;
        return cur;
    }
    ListNode* addInList(ListNode* head1, ListNode* head2) {
        //逆序
        head1=reverse(head1),head2=reverse(head2);
        ListNode *cur1=head1,*cur2=head2;
        ListNode *ret=new ListNode(0);
        ListNode *prve=ret;
        int t=0;
        while(cur1||cur2||t)
        {
            if(cur1)
            {
                t+=cur1->val;
                cur1=cur1->next;
            }
            if(cur2)
            {
                t+=cur2->val;
                cur2=cur2->next;
            }
            prve=prve->next=new ListNode(t%10);
            t/=10;
        }
        cur1=ret->next;
        delete ret;
        return reverse(cur1);

    }
};