C算法模板-＞大数减法

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#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>

using namespace std;

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

vector<int> sub(vector<int>& A, vector<int>& B)
{
    vector<int> C;
    for (int i = 0, t = 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;//判断是否退位
        else              t = 0;
    }

    while (C.size() > 1 && C.back() == 0) //去掉前导0
        C.pop_back();
        
    return C;
}
int main()
{
    string a, b;
    vector<int> A, B;
    
    cin >> a >> b;

    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');

    if (cmp(A, B))
    {
        auto C = sub(A, B);
        
        for (int i = C.size() - 1; i >= 0; i--)          printf("%d", C[i]);

    }
    else
    {
        auto C = sub(B,A);
        
        printf("-");
        
        for (int i = C.size() - 1; i >= 0; i--)          printf("%d", C[i]);
    }

    return 0;

}