HDU 4446 IT Companies

去年金华的题，现场看了一下就直接放下了。这题是直接构造答案就好了：

c[i]来自两部分，[-i+1,-1]和[i+1,n]。如果当前c[i]==0，且i最小，则说明这两段都没有比i公司要大的了，并且如果在[1,i-1]这段区间如果有比i还要大的话，那么这个i肯定不是让c[i]等于0的最小的i。所以如果当前有最小的i使c[i]==0，那么i为当前最大。如果没有的话，取最小的c[i]，这些比他大的公司都来自于[-1+1,-1]这一段，所以……

[trick] 最后一个数字后面还有空格……

/*
 Author : Speedcell
 Update : 2013-10-16
Version : soppYcell 2.4
*/

#include <algorithm>
#include <iostream>
#include <fstream>
#include <sstream>
#include <iomanip>

#include <map>
#include <set>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <string>
#include <bitset>
#include <memory>
#include <complex>
#include <numeric>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <ctype.h>
#include <assert.h>
#include <locale.h>

using namespace std;

#pragma pack(4)

#ifndef __CONSTANT__
#define __CONSTANT__

typedef long long LONG;

const double pi = acos(-1.0);
const int   inf = 0x7f7f7f7f;
const LONG  INF = 0x7f7f7f7f7f7f7f7fll;

const int go[8][2] = {{0,1},{0,-1},{1,0},{-1,0},{1,1},{1,-1},{-1,1},{-1,-1}};

#endif // __CONSTANT__

#ifndef __IO__
#define __IO__

inline bool RD(int    & a) {return scanf("%d",&a)!=EOF;}
inline bool RD(char   & a) {return scanf("%c",&a)!=EOF;}
inline bool RD(char   * a) {return scanf("%s", a)!=EOF;}
inline bool RD(double & a) {return scanf("%lf",&a)!=EOF;}
inline bool RD(LONG   & a) {return scanf("%I64d",&a)!=EOF;}

template<class T1> inline bool
    IN(T1 & a) {return RD(a);}
template<class T1,class T2> inline bool
    IN(T1 & a,T2 & b) {return RD(a)&&RD(b);}
template<class T1,class T2,class T3> inline bool
    IN(T1 & a,T2 & b,T3 & c) {return RD(a)&&RD(b)&&RD(c);}
template<class T1,class T2,class T3,class T4> inline bool
    IN(T1 & a,T2 & b,T3 & c,T4 & d) {return RD(a)&&RD(b)&&RD(c)&&RD(d);}
template<class T1,class T2,class T3,class T4,class T5> inline bool
    IN(T1 & a,T2 & b,T3 & c,T4 & d,T5 & e) {return RD(a)&&RD(b)&&RD(c)&&RD(d)&&RD(e);}
template<class T1,class T2,class T3,class T4,class T5,class T6> inline bool
    IN(T1 & a,T2 & b,T3 & c,T4 & d,T5 & e,T6 & f) {return RD(a)&&RD(b)&&RD(c)&&RD(d)&&RD(e)&&RD(f);}
template<class T1,class T2,class T3,class T4,class T5,class T6,class T7> inline bool
    IN(T1 & a,T2 & b,T3 & c,T4 & d,T5 & e,T6 & f,T7 & g) {return RD(a)&&RD(b)&&RD(c)&&RD(d)&&RD(e)&&RD(f)&&RD(g);}

inline void PT(int      a) {printf("%d",a);}
inline void PT(char     a) {printf("%c",a);}
inline void PT(char   * a) {printf("%s",a);}
inline void PT(double   a) {printf("%f",a);}
inline void PT(unsigned a) {printf("%u",a);}
inline void PT(LONG     a) {printf("%I64d",a);}
inline void PT(string   a) {printf("%s",a.c_str());}
inline void PT(const char a[]) {printf("%s",a);}

template<class T1> inline void
    OT(T1 a) {PT(a);}
template<class T1,class T2> inline void
    OT(T1 a,T2 b) {PT(a),PT(' '),PT(b);}
template<class T1,class T2,class T3> inline void
    OT(T1 a,T2 b,T3 c) {PT(a),PT(' '),PT(b),PT(' '),PT(c);}
template<class T1,class T2,class T3,class T4> inline void
    OT(T1 a,T2 b,T3 c,T4 d) {PT(a),PT(' '),PT(b),PT(' '),PT(c),PT(' '),PT(d);}
template<class T1,class T2,class T3,class T4,class T5> inline void
    OT(T1 a,T2 b,T3 c,T4 d,T5 e) {PT(a),PT(' '),PT(b),PT(' '),PT(c),PT(' '),PT(d),PT(' '),PT(e);}
template<class T1,class T2,class T3,class T4,class T5,class T6> inline void
    OT(T1 a,T2 b,T3 c,T4 d,T5 e,T6 f) {PT(a),PT(' '),PT(b),PT(' '),PT(c),PT(' '),PT(d),PT(' '),PT(e),PT(' '),PT(f);}
template<class T1,class T2,class T3,class T4,class T5,class T6,class T7> inline void
    OT(T1 a,T2 b,T3 c,T4 d,T5 e,T6 f,T7 g) {PT(a),PT(' '),PT(b),PT(' '),PT(c),PT(' '),PT(d),PT(' '),PT(e),PT(' '),PT(f),PT(' '),PT(g);}

template<class T1> inline void
    OL(T1 a) {OT(a),PT('\n');}
template<class T1,class T2> inline void
    OL(T1 a,T2 b) {OT(a,b),PT('\n');}
template<class T1,class T2,class T3> inline void
    OL(T1 a,T2 b,T3 c) {OT(a,b,c),PT('\n');}
template<class T1,class T2,class T3,class T4> inline void
    OL(T1 a,T2 b,T3 c,T4 d) {OT(a,b,c,d),PT('\n');}
template<class T1,class T2,class T3,class T4,class T5> inline void
    OL(T1 a,T2 b,T3 c,T4 d,T5 e) {OT(a,b,c,d,e),PT('\n');}
template<class T1,class T2,class T3,class T4,class T5,class T6> inline void
    OL(T1 a,T2 b,T3 c,T4 d,T5 e,T6 f) {OT(a,b,c,d,e,f),PT('\n');}
template<class T1,class T2,class T3,class T4,class T5,class T6,class T7> inline void
    OL(T1 a,T2 b,T3 c,T4 d,T5 e,T6 f,T7 g) {OT(a,b,c,d,e,f,g),PT('\n');}

#endif // __IO__

#ifndef __MACRO__
#define __MACRO__

#define ML(times) int tcase; IN(tcase); FOR(times,1,tcase)

#define FOR(i,a,b) for(int i=int(a),_##i=int(b);i<=_##i;i++)
#define DWN(i,b,a) for(int i=int(b),_##i=int(a);_##i<=i;i--)
#define ECH(i,u,pre,next) for(int i=int(pre[u]);i!=-1;i=int(next[i]))

#define MEM(a,v) memset(a,v,sizeof(a))
#define CLR(a,v) FOR(_i##a,0,sizeof(a)/sizeof(a[0])-1) a[_i##a]=v

#define LOOP(a,n)                                               \
    FOR(_i##a,0,(n)-1)                                          \
        OT(a[_i##a]),OT(_i##a!=__i##a?' ':'\n')
#define LOOP2(a,n,m)                                            \
    FOR(_i##a,0,(n)-1) FOR(_j##a,0,(m)-1)                       \
        OT(a[_i##a][_j##a]),OT(_j##a!=__j##a?' ':'\n')
#define LOOPG(G,n,pre,next)                                     \
    FOR(_i##a,0,(n)-1) ECH(_j##a,_i##a,pre,next)                \
        OL(_i##a,G[_j##a].v,G[_j##a].w)

#endif // __MACRO__

#ifndef __BIT__
#define __BIT__

template<class T> inline T lb(T i) {return i&-i;}
template<class T> inline T lc(T i) {return i<<1;}
template<class T> inline T rc(T i) {return i<<1|1;}
template<class T> inline T at(T a,int i) {return a& (T(1)<<i);}
template<class T> inline T nt(T a,int i) {return a^ (T(1)<<i);}
template<class T> inline T s1(T a,int i) {return a| (T(1)<<i);}
template<class T> inline T s0(T a,int i) {return a&~(T(1)<<i);}

#endif // __BIT__

#ifndef __COMPARER__
#define __COMPARER__

const double eps = 1e-8;

inline int cmp(double a,double b=0) {return fabs(b-a)<eps?0:((b-a)<eps?+1:-1);}
template<typename type> inline int cmp(type a,type b=0) {return a==b?0:(b<a?+1:-1);}

template<typename type> inline bool gt(type a,type b) {return cmp(a,b)> 0;}
template<typename type> inline bool ge(type a,type b) {return cmp(a,b)>=0;}
template<typename type> inline bool eq(type a,type b) {return cmp(a,b)==0;}
template<typename type> inline bool ne(type a,type b) {return cmp(a,b)!=0;}
template<typename type> inline bool le(type a,type b) {return cmp(a,b)<=0;}
template<typename type> inline bool ls(type a,type b) {return cmp(a,b)< 0;}

template<typename type> inline type smax(type a,type b) {return gt(a,b)?a:b;}
template<typename type> inline type smin(type a,type b) {return ls(a,b)?a:b;}

#endif // __COMPARER__

const int MAXV = 240000;

class SegmentTree
{
private:
	int L,R,val[MAXV<<2],label[MAXV<<2],lazy[MAXV<<2];

	#define ls(l,r,i) l,(l+r)/2,lc(i)
	#define rs(l,r,i) (l+r)/2+1,r,rc(i)

	void add(int v,int l,int r,int i)
	{
		if(l<=r) val[i]+=v,lazy[i]+=v;
	}
	void down(int l,int r,int i)
	{
		if(l<r&&lazy[i])
		{
			add(lazy[i],ls(l,r,i));
			add(lazy[i],rs(l,r,i));
			lazy[i]=0;
		}
	}
	void up(int l,int r,int i)
	{
		if(l<r)
		{
			if(val[lc(i)]<=val[rc(i)])
			{
				val[i]=val[lc(i)];
				label[i]=label[lc(i)];
			}
			else
			{
				val[i]=val[rc(i)];
				label[i]=label[rc(i)];
			}
		}
	}
	void update_set(int x,int v,int l,int r,int i)
	{
		if(x==l&&r==x) val[i]=v,label[i]=x;
		else
		{
			down(l,r,i);
			if(x<=(l+r)/2) update_set(x,v,ls(l,r,i));
			else update_set(x,v,rs(l,r,i));
			up(l,r,i);
		}
	}
	void update_add(int x,int y,int v,int l,int r,int i)
	{
		if(x<=l&&r<=y) add(v,l,r,i);
		else
		{
			down(l,r,i);
			if(x<=(l+r)/2) update_add(x,y,v,ls(l,r,i));
			if((l+r)/2<y) update_add(x,y,v,rs(l,r,i));
			up(l,r,i);
		}
	}
public:
	void clear(int l,int r)
	{
		L=l;
		R=r;
		MEM(lazy,0);
		MEM(val,inf);
		MEM(label,inf);
	}
	void update_set(int x,int v)
	{
		update_set(x,v,L,R,1);
	}
	void update_add(int x,int y,int v)
	{
		if(x<=y) update_add(x,y,v,L,R,1);
	}
	int query_val(void)
	{
		return val[1];
	}
	int query_label(void)
	{
		return label[1];
	}
}st;

deque<int> a,b;
int n,c,ans[MAXV];

bool solve(void)
{
	while(!a.empty()) a.pop_front();
	while(!b.empty()) b.pop_front();
	FOR(i,1,n)
	{
		int v=st.query_label();
		int w=st.query_val();
		if(w==0)
		{
			a.push_back(v);
			b.push_back(-v);
			st.update_add(1,v-1,-1);
			st.update_set(v,inf);
		}
		else if(w>0)
		{
			if(b.empty()) return false;
			else
			{
				i--;
				v=b.front();
				b.pop_front();
				a.push_back(v);
				st.update_add(-v+1,n,-1);
			}
		}
		else return false;
	}
	return true;
}

int main()
{
    #ifndef ONLINE_JUDGE
    freopen("IT Companies.txt","r",stdin);
    #else
    #endif

    while(IN(n),n)
	{
		st.clear(1,n);
		FOR(i,1,n) IN(c),st.update_set(i,c);
		if(!solve()) OL("Impossible");
		else
		{
			while(!b.empty())
			{
				a.push_back(b.front());
				b.pop_front();
			}
			int cnt=0;
			while(!a.empty())
			{
				ans[cnt++]=a.back();
				a.pop_back();
			}
			FOR(i,0,cnt-1) OT(ans[i],"");
			OL("");
		}
	}

    return 0;
}