37 lines
690 B
C++
37 lines
690 B
C++
#include<cstdio>
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unsigned long long ans=0;
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void fsort(int *left,int *right,bool (*cmp)(int a,int b),int *k)
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{
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if(right-left<=1) return;
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unsigned int len=right-left;
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fsort(left,left+len/2,cmp,k);
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fsort(left+len/2,right,cmp,k+len/2);
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int i=0,j=len/2,n=0;
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while(i<len/2&&j<len)
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{
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if(cmp(left[i],left[j])) k[n++]=left[i++];
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else
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{
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k[n++]=left[j++];
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ans+=len/2-i;
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}
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}
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while(i<len/2) k[n++]=left[i++];
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while(j<len) k[n++]=left[j++];
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for(int i=0;i<len;i++) left[i]=k[i];
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}
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bool cmp(int a,int b)
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{
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return a<=b;
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}
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int main()
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{
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int n;
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scanf("%d",&n);
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int num[n],f[n];
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for(int i=0;i<n;i++) scanf("%d",num+i);
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fsort(num,num+n,cmp,f);
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printf("%lld\n",ans);
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return 0;
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}
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