python/TangDou/AcWing/HighPrecision/792_sub.cpp

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

const int N = 1e5 + 10;
int a[N], al;
int b[N], bl;

void sub(int a[], int &al, int b[], int &bl) {
    int t = 0;
    al = max(al, bl);
    for (int i = 0; i < al; i++) {
        t = a[i] - b[i] - t;
        a[i] = (t + 10) % 10;
        t < 0 ? t = 1 : t = 0;
    }
    while (al > 0 && a[al] == 0) al--;
}

int main() {
    string x, y;
    cin >> x >> y;

    // 负号
    if (x.size() < y.size() || (x.size() == y.size() && x < y)) {
        printf("-");
        swap(x, y);
    }

    for (int i = x.size() - 1; i >= 0; i--) a[al++] = x[i] - '0';
    for (int i = y.size() - 1; i >= 0; i--) b[bl++] = y[i] - '0';

    sub(a, al, b, bl);

    for (int i = al; i >= 0; i--) printf("%d", a[i]);
    return 0;
}