Sort it

http://acm.hdu.edu.cn/showproblem.php?pid=2689

C++版本一

线段树

/*
*@Author:   STZG
*@Language: C++
*/
//#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
int ans,cnt,flag,temp;
ll tree[N<<2];
void pushup(int rt){
    tree[rt]=tree[rt<<1]+tree[rt<<1|1];
}
void updata(int l,int r,int rt,int L,int C){
    if(l==r){
        tree[rt]+=C;
        return;
    }
    int mid=(l+r)>>1;
    if(L<=mid)updata(l,mid,rt<<1,L,C);
    else updata(mid+1,r,rt<<1|1,L,C);
    pushup(rt);
}
ll query(int l,int r,int rt,int L,int R){
    if(l>=L&&r<=R){
        return tree[rt];
    }
    int mid=(l+r)>>1;
    ll res=0;
    if(L<=mid)res+=query(l,mid,rt<<1,L,R);
    if(R>mid)res+=query(mid+1,r,rt<<1|1,L,R);
    return res;
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    while(~scanf("%d",&n)){
        memset(tree,0,sizeof(tree));
        ans=0;
        for(int i=1;i<=n;i++){
            scanf("%d",&t);
            ans+=query(1,n,1,t+1,n);
            updata(1,n,1,t,1);
        }
        cout << ans << endl;
    }
    //cout << "Hello world!" << endl;
    return 0;
}

C++版本二

树状数组

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
inline int read()
{
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9')
    {
        if(ch=='-')
            f=-1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9')
    {
        x=x*10+ch-'0';
        ch=getchar();
    }
    return x*f;
}
inline void write(int x)
{
    if(x<0)
    {
        putchar('-');
        x=-x;
    }
    if(x>9)
    {
        write(x/10);
    }
    putchar(x%10+'0');
}
const int N=1001;
int n;
int num[N];
int c[N];
struct node
{
    int x;
    int id;
}q[N] ;
bool cmp(node a,node b)
{
    return a.x<b.x;
}
int lowbit(int x)
{
    return x&(-x);
}
int getsum(int x)
{
    int s=0;
    while(x>0)
    {
        s+=c[x];
        x-=lowbit(x);
    }
    return s;
}
void add(int x,int y)
{
    while(x<=n)
    {
        c[x]+=y;
        x+=lowbit(x);
    }
}
int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        memset(c,0,sizeof(c));
        memset(num,0,sizeof(num));
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&q[i].x);
            q[i].id=i;
        }
        sort(q+1,q+1+n,cmp);
        for(int i=1;i<=n;i++)
        {
            num[q[i].id]=i;
        }
        int sum = 0;
        for(int i=1;i<=n;i++)
        {
            add(num[i],1);
            sum+=getsum(n)-getsum(num[i]);
        }
        printf("%d\n",sum);
    }
    return 0;
}

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