Go: package main

import (
	"bufio"
	"os"
	"strings"
	"strconv"
	"fmt"
)

var scanner = bufio.NewScanner(os.Stdin)

const INF = 0x7FFFFFFF

func main() {
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		n, _ := strconv.Atoi(buf[0])
		m, _ := strconv.Atoi(buf[1])
		if n == 0 && m == 0 {
			break
		}
		chair := make([]string, n+1)
		for i := range chair {
			chair[i] = "#"
		}
		chair[n] = "Sentinel"
		for i := 0; i < m; i++ {
			scanner.Scan()
			switch who := scanner.Text(); who {
			case "A": // 左から眺めて行って空いている席があったら即座に座る
				for j := 0; j < n; j++ {
					if chair[j] == "#" {
						chair[j] = "A"
						break
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "B":
				flag := true
				// 右端からAの隣でない席を探していく
				for j := n-1; j > -1; j-- {
					if chair[j] == "#" && (j == 0 || chair[j-1] != "A") && chair[j+1] != "A" {
						flag = false
						chair[j] = "B"
						break
					}
				}
				// Aの隣しか空いていないので一番左端の空いている席に座る
				if flag {
					for j := 0; j < n; j++ {
						if chair[j] == "#" {
							chair[j] = "B"
							break
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "C":
				if i == 0 {
					chair[n/2] = "C" // 先客が誰もいないときは真ん中の椅子に座る
				} else {
					for j := 0; j < n; j++ { // 左から舐めて
						if chair[j] != "#" { // その席が空いていなくて
							if chair[j+1] == "#" { // 右隣が空いているなら座る
								chair[j+1] = "C"
								break
							} else if j != 0 && chair[j-1] == "#" { // 右隣が空いていないので左隣に座る
								chair[j-1] = "C"
								break
							}
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "D":
				distanceTable := make([]int ,n)
				for j := range distanceTable {
					distanceTable[j] = INF
				}
				for j:= 0; j < n; j++ {
					if chair[j] != "#" {
						for k := 0; k < n; k++ {
							distanceTable[k] = min(distanceTable[k], abs(j-k))
						}
					}
				}
				// log.Println("distanceTAble:", distanceTable)
				at := 0
				distance := 0
				for j := 0; j < n; j++ {
					if distance < distanceTable[j] {
						at = j
						distance = distanceTable[j]
					}
				}
				chair[at] = "D"
				// log.Println(chair)
				break // 次の人を読み込む
			}
		}
		fmt.Println(strings.Join(chair, ""))
	}
}

func min(a, b int) int {
	if a > b {
		return b
	}
	return a
}

func abs(a int) int {
	if a < 0 {
		return -a
	}
	return a
}

C++: 
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<cassert>
#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<numeric>
#include<algorithm>
#include<bitset>
#include<complex>

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
#define mp make_pair

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cout << *i << " "; cout << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

int chairs[110];
int n,m;

void fa(){
	int i;
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			chairs[i]=1;
			return;
		}
	}
}

void fb(){
	int i;
	for(i=n-1;i>=0;i--){
		if(chairs[i]==0&&(i==n-1||chairs[i+1]!=1)&&(i==0||chairs[i-1]!=1)){
			chairs[i]=2;
			return;
		}
	}
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			chairs[i]=2;
			return;
		}
	}
}

void fc(){
	int i;
	for(i=0;i<n;i++){
		if(chairs[i]==0)continue;
		if(i!=n-1&&chairs[i+1]==0){
			chairs[i+1]=3;
			return;
		}
		if(i!=0&&chairs[i-1]==0){
			chairs[i-1]=3;
			return;
		}
	}
	if(n%2==0){
		chairs[n/2]=3;
		return;
	}else{
		chairs[(n+1)/2-1]=3;
		return;
	}
}

void fd(){
	int i,j;
	int c=0,d=0,dd;
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			for(j=1;i-j>=0;j++){
				if(chairs[i-j]!=0)break;
			}
			if(i-j<0)j=n;
			dd=j;
			for(j=1;i+j<n;j++){
				if(chairs[i+j]!=0)break;
			}
			if(i+j==n)j=n;
			chmin(dd,j);
			if(d<dd){
				c=i;
				d=dd;
			}
		}
	}
	chairs[c]=4;
	return;
}

int main() {
	while(cin>>n>>m,n){
		int i;
		string str;
		for(i=0;i<n;i++)chairs[i]=0;
		for(i=0;i<m;i++){
			cin>>str;
//cout<<str;
			if(str[0]=='A')fa();
			if(str[0]=='B')fb();
			if(str[0]=='C')fc();
			if(str[0]=='D')fd();
		}
//cout<<" : ";
		for(i=0;i<n;i++){
			if(chairs[i]==0)cout<<"#";
			else if(chairs[i]==1)cout<<"A";
			else if(chairs[i]==2)cout<<"B";
			else if(chairs[i]==3)cout<<"C";
			else if(chairs[i]==4)cout<<"D";
		}
		cout<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<algorithm>
using namespace std;

int main(){
  int n,m;

  for(;;){
    cin >> n >> m;
    if(!n && !m)break;

    string c;
    for(int i=0;i<n;i++)c += '#';

    for(int i=0;i<m;i++){
      char g;
      cin >> g;

      int pos;
      if(g == 'A'){
	pos = 0;
	while(c[pos]!='#')pos++;
      }else if(g == 'B'){
	pos = n-1;
	while(pos>=0){
	  if(c[pos]=='#'){
	    if( (pos==n-1 || c[pos+1]!='A') && (pos==0 || c[pos-1]!='A') )break;
	  }
	  pos--;
	}
	if(pos<0){
	  pos = 0;
	  while(c[pos]!='#')pos++;
	}
      }else if(g == 'C'){
	if(!i)pos = n/2;
	else{
	  pos = 0;
	  while(pos<n){
	    if(c[pos]!='#'){
	      if(pos<n-1 && c[pos+1]=='#'){
		pos++;
		break;
	      }
	      if(pos>0 && c[pos-1]=='#'){
		pos--;
	      break;
	      }
	    }
	    pos++;
	  }
	}
      }else{
	pos = 0;
	if(i){
	  int dis = 0;
	  int tmp = -1;
	  while(pos<n){
	    if(c[pos]=='#'){
	      int l = 1,r = 1;
	      while(pos-l>=0 && c[pos-l]=='#')l++;
	      while(pos+r<n && c[pos+r]=='#')r++;
	      if(pos-l<0){
		if(dis<r){
		  dis = r;
		  tmp = pos;
		}
	      }else if(pos+r>=n){
		if(dis<l){
		  dis = l;
		  tmp = pos;
		}
	      }else{
		if(dis<min(l,r)){
		  dis = min(l,r);
		  tmp = pos;
		}
	      }
	    }
	    pos++;
	  }
	  pos = tmp;
	}
      }
      c[pos] = g;
    }

    cout << c << endl;
  }
}

C++: #include <iostream>
#include <set>
#include <vector>
#include <string>
#include <utility>
#include <algorithm>
#include <stdio.h>
using namespace std;
typedef pair<int,int> P;
int chair[110];
int n,m;
void A(){
	int ans=0;
	while(chair[ans]!=0)ans++;
	chair[ans]=1;
	return;
}
void B(){
	for(int i=n-1;i>=0;i--){
		if(chair[i]==0){
			if(i==0&&chair[1]!=1){chair[0]=2;return;}
			else if(i==n-1&&chair[n-2]!=1){chair[n-1]=2;return;}
			else if(0<i&&i<n-1&&chair[i-1]!=1&&chair[i+1]!=1){chair[i]=2;return;}
		}
	}
	int ans=0;
	while(chair[ans]!=0)ans++;
	chair[ans]=2;
	return;
}
void C(){
	int ans=0;
	if(chair[0]!=0){
		while(chair[ans]!=0)ans++;
		chair[ans]=3;
		return;
	}
	chair[n]=5;
	for(int i=0;i<n;i++){
		if(chair[i]!=0){
			if(chair[i+1]==0)chair[i+1]=3;
			else chair[i-1]=3;
			return;
		}
	}
	if(n%2)chair[(n+1)/2-1]=3;
	else chair[n/2]=3;
	return;
}
void D(){
	int a=0,f=0;
	P bl[52];
	bool in=false;
	for(int i=0;i<=n;i++){
		if(in&&chair[i]!=0){
			in=false;bl[a++]=P(f,i);
		}else if(!in&&chair[i]==0){
			in=true;f=i;
		}
	}
	//for(int i=0;i<a;i++)printf("bl[%d]:[%d,%d)\n",i,bl[i].first,bl[i].second);
	if(bl[0].first==0&&bl[0].second==n){
		chair[0]=4;return;
	}else{
		int m,mlen=0;
		for(int i=0;i<a;i++){
			int dis=(bl[i].second-bl[i].first-1)/2;
			if(bl[i].second==n)dis=bl[i].second-bl[i].first-1;
			if(dis>mlen){
				mlen=bl[i].second-bl[i].first;m=i;
			}
		}
		chair[bl[m].first+mlen]=4;return;
	}
}
int main()
{
	while(cin>>n>>m&&(n||m)){
		fill(chair,chair+n,0);
		chair[n]=5;
		while(m--){
			char c;cin>>c;
			if(c=='A')A();
			if(c=='B')B();
			if(c=='C')C();
			if(c=='D')D();
		}
		for(int i=0;i<n;i++){
			if(chair[i]==0)cout<<'#';
			if(chair[i]==1)cout<<'A';
			if(chair[i]==2)cout<<'B';
			if(chair[i]==3)cout<<'C';
			if(chair[i]==4)cout<<'D';
		}
		cout<<endl;
	}
    return 0;
}