POJ 2299Ultra-QuickSort

题意：线段树求逆序对经典题目，需要离散处理，但是用stl处理的话会T，手动二分处理即可；

#include<algorithm>
#include<iostream>
#include<map>
#include<set>
#include<vector>
#include<queue>
#include<stack>
#include<cstring>
#include<cstdio>
#define N 500005
using namespace std;
typedef struct node{
	int x;int y;int date;
}node;
bool cmp(int a,int b){
	return a>b;
}
node a[4*N];
void built(int root,int first,int end){
	if(first==end){
		a[root].x=first;a[root].y=end;a[root].date=0;
		return ;
	}
	int mid=(first+end)/2;
	built(root*2,first,mid);
	built(root*2+1,mid+1,end);
	a[root].x=a[root*2].x;a[root].y=a[root*2+1].y;a[root].date=0;
}
void U(int root,int first,int end,int e){
	if(first==end){
		a[root].date++;
		return ;
	}
	int mid=(first+end)/2;
	if(e<=mid)  U(root*2,first,mid,e);
	else U(root*2+1,mid+1,end,e);
	a[root].date=a[root*2].date+a[root*2+1].date;
}
long long sum=0;
void Q(int root,int first,int end,int l,int r){
	if(l<=first&&end<=r){
		sum+=a[root].date;
		return ;
	}
	int mid=(first+end)/2;
	if(l<=mid)  Q(root*2,first,mid,l,r);
	if(r>mid)  Q(root*2+1,mid+1,end,l,r);
}
long long b[N];
long long c[N];
long long e[N];
long long p[N];
int main(){
	int m;
	while(scanf("%d",&m)==1&&m!=0){
		for(int i=1;i<=m;i++){
			scanf("%d",&b[i]);
			p[i]=b[i];
		}
		sort(b+1,b+m+1,cmp);
		e[1]=b[1];
		int k=1;
		for(int i=2;i<=m;i++){
			if(b[i]!=b[i-1]){
				k++;
				e[k]=b[i];
			}
		}
		for(int i=1;i<=m;i++){
			int first=1;int end=k;
			while(first<=end){
				int mid=(first+end)/2;
				if(p[i]==e[mid]){
					c[i]=mid;
					break;
				}
				else if(p[i]<e[mid]){
					first=mid+1;
				}
				else{
					end=mid-1;
				}
			}
		}
		built(1,1,k);
		long long ans=0;
	  for(int i=1;i<=m;i++){
	  	sum=0;
	  	if(c[i]==1){
	  		U(1,1,k,c[i]);
		  }
		  else{
	  	Q(1,1,k,1,c[i]-1);
	  	ans+=sum;
	  	U(1,1,k,c[i]);}
	  }
	  printf("%lld\n",ans);
	}
	return 0;
}