hdu 2852 树状数组

查找比a大的第k小的元素其实就是查找第sum(a)+k小的元素，用不需要二分的树状数组就可以了。

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

const int N = 100000;
int c[N];

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

void update( int i, int v )
{
    while ( i < N )
    {
        c[i] += v;
        i += lb(i);
    }
}

int sum( int i )
{
    int ans = 0;
    while ( i )
    {
        ans += c[i];
        i -= lb(i);
    }
    return ans;
}

int sumk( int k )
{
    int ans = 0, cnt = 0;
    for ( int i = 20; i >= 0; i-- )
    {
        ans += ( 1 << i );
        if ( ans >= N - 1 || cnt + c[ans] >= k )
        {
            ans -= ( 1 << i );
        }
        else
        {
            cnt += c[ans];
        }
    }
    return ans + 1;
}

int main ()
{
    int n;
    while ( scanf("%d", &n) != EOF )
    {
        memset( c, 0, sizeof(c) );
        for ( int i = 1; i <= n; i++ )
        {
            int op, x, y;
            scanf("%d", &op);
            if ( op == 0 )
            {
                scanf("%d", &x);
                update( x, 1 );
            }
            else if ( op == 1 )
            {
                scanf("%d", &x);
                if ( sum(x) - sum( x - 1 ) > 0 )
                {
                    update( x, -1 );
                }
                else
                {
                    printf("No Elment!
");
                }
            }
            else
            {
                scanf("%d%d", &x, &y);
                int k = sum(x) + y;
                if ( k <= sum( N - 1 ) )
                {
                    printf("%d
", sumk(k));
                }
                else
                {
                    printf("Not Find!
");
                }
            }
        }
    }
    return 0;
}