43 lines
985 B
C++
43 lines
985 B
C++
#include<cstdio>
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#include<cstring>
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#include<algorithm>
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using namespace std;
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#define x first
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#define y second
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typedef long long LL;
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const LL mod=1000000007;
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const int maxn=2010;
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pair<int,int> a[maxn];
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int h,w,n;
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LL f[maxn],jc[200010],ijc[200010];
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inline LL C(int n,int m) { return jc[n]*ijc[m]%mod*ijc[n-m]%mod; }
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inline LL ksm(LL a,LL b)
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{
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LL res=1;
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for(;b;b>>=1,a=a*a%mod) b&1?res=res*a%mod:0;
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return res;
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}
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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jc[0]=1; ijc[0]=1;
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for(int i=1;i<=200000;i++) { jc[i]=jc[i-1]*i%mod; ijc[i]=ksm(jc[i],mod-2); }
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scanf("%d%d%d",&h,&w,&n);
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for(int i=1;i<=n;i++) scanf("%d%d",&a[i].x,&a[i].y);
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sort(a+1,a+1+n);
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a[n+1].x=h; a[n+1].y=w;
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for(int i=1;i<=n+1;i++)
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{
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f[i]=C(a[i].x+a[i].y-2,a[i].x-1);
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for(int j=1;j<i;j++)
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{
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if(a[j].x>a[i].x||a[j].y>a[i].y) continue;
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f[i]=(f[i]-(LL)f[j]*C(a[i].x+a[i].y-a[j].x-a[j].y,a[i].x-a[j].x))%mod;
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f[i]=f[i]<0?f[i]+mod:f[i];
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}
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}
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printf("%lld\n",f[n+1]);
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return 0;
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} |