暑期ACM队内练习赛 H题 数字游戏

program：

#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

const int MAXN = 500005;

char s[MAXN], a[MAXN];
vector< int > v[10];

int main( void )
{
// freopen( "d.in","r",stdin );
// freopen( "out.txt","w",stdout );

int n, k,t;
scanf("%d",&t);
while(t--)
{
for(int i=0;i<10;i++)
v[i].clear();
scanf( "%d %d", &n, &k );
scanf( "%s", s );

for( int i = n-1; i >= 0; --i )
v[ s[i]-'0' ].push_back( i );

int m = n-k, p = 0;
for( int i = 0; i < m; ++i )
{
//biramo n-k znamenaka
for( int j = 9; j >= 0; --j )
{
while( v[j].size() > 0 && v[j].back() < p )
v[j].pop_back();
if( v[j].size() > 0 && n-v[j].back()-1 >= m-i-1 )
{
p = v[j].back();
break;
}
}
a[i] = s[p];
p++;
}

a[m] = '\0';
puts( a );
}
return 0;
}