求逆序对个数。我是用离散化+树状数组做的。
以下是我的代码：
/*
* Author: lee1r
* Created Time: 2011/8/5 23:33:01
* File Name: poj2299.cpp
*/
#include<iostream>
#include<sstream>
#include<fstream>
#include<vector>
#include<list>
#include<deque>
#include<queue>
#include<stack>
#include<map>
#include<set>
#include<bitset>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cctype>
#include<cmath>
#include<ctime>
#define L(x) ((x)<<1)
#define R(x) (((x)<<1)+1)
#define Half(x) ((x)>>1)
#define lowbit(x) ((x)&(-(x)))
using namespace std;
const int kInf(0x7f7f7f7f);
const double kEps(1e-8);
typedef long long int64;
typedef unsigned long long uint64;
const int kMaxn(500007);
struct Type
{
int id,value,num;
};
bool cmp1(const Type &a,const Type &b)
{
return a.value<b.value;
}
bool cmp2(const Type &a,const Type &b)
{
return a.id<b.id;
}
int n,bit[kMaxn];
Type r[kMaxn];
int64 ans;
void Add(int x,int delta)
{
for(int i=x;i<=n;i+=lowbit(i))
bit[i]+=delta;
}
int Sum(int x)
{
int re(0);
for(int i=x;i>0;i-=lowbit(i))
re+=bit[i];
return re;
}
int main()
{
//freopen("data.in","r",stdin);
while(scanf("%d",&n)==1 && n)
{
for(int i=1;i<=n;i++)
{
scanf("%d",&r[i].value);
r[i].id=i;
}
sort(r+1,r+n+1,cmp1);
for(int i=1;i<=n;i++)
r[i].num=i;
sort(r+1,r+n+1,cmp2);
ans=0;
memset(bit,0,sizeof(bit));
for(int i=1;i<=n;i++)
{
Add(r[i].num,1);
ans+=i-Sum(r[i].num-1)-1;
}
cout<<ans<<endl;
}
return 0;
}
posted on 2011-08-05 23:44
lee1r 阅读(250)
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题目分类：数据结构