题目描述

大数的减法 C++

样例

#include <iostream>
#include <string>
#include <vector>
using namespace std;

// 比较A和B的大小
bool isBig(string A,string B)
{
    if (A.size() > B.size()) return true;
    else if (A.size() < B.size()) return false;
    else
    {
        for (int i=0;i<A.size();i++)
        {
            if (A[i] > B[i]) return true;
            else if (A[i] < B[i]) return false;
        }
    }
    return true;
}

vector<int> substractBigNum(vector<int> vecA, vector<int> vecB)
{
    vector<int> VecTemp;
    int t = 0;//用于记录借位
    for (int i=0;i<vecA.size();i++)
    {
        if (i < vecB.size())
        {
            VecTemp.push_back((vecA[i] - vecB[i] - t + 10) % 10);
            if (vecA[i] - vecB[i] - t < 0) t = 1;
            else t = 0;
        }
        else
        {
            VecTemp.push_back((vecA[i] - t + 10) % 10);
            if (vecA[i] - t < 0) t = 1;
            else t = 0;
        }
    }
    while(VecTemp.size() > 1 && VecTemp.back() == 0) VecTemp.pop_back();
    return VecTemp;
}

int main()
{
    string A, B;
    cin >> A >> B;

    vector<int> vecA, vecB;
    for (int i= A.size() - 1;i >= 0;i--)
    {
        vecA.push_back(A[i] - '0');
    }
    for (int i = B.size() - 1; i >= 0; i--)
    {
        vecB.push_back(B[i] - '0');
    }
    vector<int> ans;
    if (isBig(A,B))
    {
        ans = substractBigNum(vecA,vecB);
    }
    else
    {
        ans = substractBigNum(vecB, vecA);
        cout << "-";
    }

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