"Inspur Cup" Shandong Province 8th ACM College Students Programming Contest fireworks (number of combinations)

One of the pits, using lucas to generate the number of combinations is always wrong. Later, I saw that others used the inverse element to generate it, so I used the inverse element, and found that the inverse element is really amazingly fast. I still didn't think about the complexity seriously. When I saw lucas, I wanted to set the template, and I didn't think about the complexity at all.

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5+7;
int mod = 1e9+7;
typedef unsigned long long LL;
LL jie[110000];

void init()
{
    jie[0]=jie[1]=1;
    for(int i=2; i<=100000; i++)
        they [i] = (they [i-1] * i)% mod;
}

LL mult(LL a,LL n)
{
    LL ans=1;
    while(n)
    {
        if(n&1)ans=(ans*a)%mod;
        a=(a*a)%mod;
        n>>=1;
    }
    return ans;
}

LL C(LL n,LL m)
{
    return (jie [n] * mult (jie [nm], mod-2))% mod * mult (jie [m], mod-2))% mod;
}

int x,val;
intmain()
{
    init();
 int n,t,w;
 while(~scanf("%d%d%d",&n,&t,&w))
 {
     LL ans=0;

     for(int i=1;i<=n;i++)
     {
         scanf("%d%d",&x,&val);
         x-=t;
         if(w<x)continue;
         int tmp=w-x;
         if(tmp%2)continue;
         tmp/=2;
         if(tmp>t)continue;
         //cout<<tmp<<endl;
         if(tmp*2>t)
            tmp=t-tmp;
         ans+=C(t,tmp)*val;
         ans% = mod;
     }
    printf("%lld\n",ans);
 }
    return 0;
}