高精度乘高精度

注意处理输入的负数

高精度模板背熟

#include<bits/stdc++.h>
#define int long long
using namespace std;

vector<int> A,B;
string a,b;

bool cmp(vector<int> &A,vector<int> &B)
{
    if(A.size() != B.size())return A.size()>B.size();
    else
    {
        for(int i = A.size()-1;i>=0;i--)
        {
            if(A[i] != B[i])return A[i] > B[i];
        }
    }
    return true;
}

vector<int> mul(vector<int> &A,vector<int> &B)
{
    vector<int> C(A.size() + B.size());
    for(int i = 0;i<A.size();i++)
    {
        for(int j = 0;j<B.size();j++)
        {
            C[i+j] += A[i] * B[j];
        }
    }

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

    while(C.size() > 1 && C.back() == 0)C.pop_back();
    return C;
}

vector<int> sub(vector<int> &A,vector<int> &B)
{
    vector<int> C;
    int t = 0;
    for(int i = 0;i<A.size();i++)
    {
        t = A[i] - t;
        if(i < B.size())t -= B[i];
        C.push_back((t+10) % 10);

        if(t < 0)t = 1;
        else t = 0;
    }
    while(C.size() > 1 && C.back() == 0)C.pop_back();
    return C;
}

signed main()
{
  string aa,bb,a,b;

   cin>>aa>>bb;

  if(aa[0] == '-') 
      for(int i = 1; i < aa.size(); i++) a += aa[i];
  else a = aa;
  if(bb[0] == '-') 
      for(int i = 1; i < bb.size(); i++) b += bb[i];
  else b = bb;

    for(int i = a.size()-1;i>=0;i--)A.push_back(a[i] - '0');
    for(int i = b.size()-1;i>=0;i--)B.push_back(b[i] - '0');

    vector<int> C = mul(A,A);
    vector<int> D = mul(B,B);

    vector<int> ans;
    if(cmp(C,D))ans = sub(C,D);
    else 
  {
    cout<<"-";
    ans = sub(D,C);
  }

    for(int i = ans.size()-1;i>=0;i--)cout<<ans[i];
    return 0;
}