学步园

与2299类似，求逆序数；

首先按x升序排列，再求y的逆序数；

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <stdlib.h>

using namespace std;

int b[1000005];
int n,m,k;

struct q
{
    int x;
    int y;
}p[1000105];

bool cmp(q a ,q b)
{
    if (a.x != b.x)
        return a.x < b.x;
    else
        return a.y <= b.y;
}

int lowbit(int i)
{
    return i&-i;
}

int sum(int i)
{
    long long  ans =0;
    while (i>0)
    {
        ans += b[i];
        i -= lowbit(i);
    }
    return ans;
}

void update(int i,int v)
{
    while (i<=m)
    {
        b[i]+=v;
        i+=lowbit(i);
    }
}

int main ()
{
    int t ;
    int ss=1;
    scanf ("%d",&t);
    while (t--)
    {
        scanf ("%d%d%d",&n,&m,&k);
        for (int i=1;i<=k;i++)
        {
            scanf ("%d%d",&p[i].x,&p[i].y  );
        }

        sort (p+1,p+1+k,cmp);

        memset(b,0,sizeof(b));
        long long  ans =0 ;
        for (int i=1;i<=k;i++)
        {
            update(p[i].y,1);
            ans += i-sum( p[i].y );
        }

        printf("Test case %d: ",ss++);
        printf("%lld\n",ans);
    }
    return 0;
}