有些时候确实挺无助的

此题需要前置知识——扩展欧几里得算法（exgcd）

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

const int N = 15;
int a[N],r[N],k;

int exgcd(int a, int b, int &x, int &y)
{
    if(b == 0)
    {
        x = 1; 
        y = 0;
        return a;
    }
    int ans = exgcd(b, a % b, x, y);
    int t = x;
    x = y;
    y = t - a / b * y;
    return ans;
}

int crt(int k, int* a, int* r)
{
    int n = 1, ans = 0;
    for(int i = 1; i <= k; i++) n = n * r[i];
    for (int i = 1; i <= k; i++)
    {
        int m = n / r[i], b, y;
        exgcd(m, r[i], b, y);
        ans = (ans + a[i] * m * b % n) % n;
    }
    return (ans % n + n) % n;
}


signed main()
{
    scanf("%lld",&k);
    for(int i=1;i<=k;i++) scanf("%lld%lld",&a[i],&r[i]);
    printf("%lld",crt(k,a,r));
    return 0;
}