delete pics to save space

history_source/信息学奥赛一本通/2.7.4.cpp

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