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
			}
		}
		for i := 0; i < n; i++ {
			if i == n-1 {
				fmt.Println(chair[i])
			} else {
				fmt.Printf("%s ", chair[i])
			}
		}
	}
}

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 <iostream>
#include <vector>
#include <algorithm>

int main() {
	int n, m;
	const char output[] = { '#', 'A', 'B', 'C', 'D' };
	std::vector<int> seat;
	
	while (std::cin >> n >> m) {
		if (n == 0 && m == 0)
			break;

		seat.resize(n);

		for (int i = 0; i < m; ++i) {
			char who;
			std::cin >> who;

			if (who == 'A') {
				for (int j = 0; j < n; ++j) {
					if (seat[j] == 0) {
						seat[j] = 1;
						break;
					}
				}
			}
			else if (who == 'B') {
				int firstEmpty = 334;
				bool isRightA = false;

				for (int j = n - 1; j >= 0; --j) {
					if (seat[j] == 0) {
						firstEmpty = std::min(firstEmpty, j);
						if (!isRightA && (j == 0 || seat[j - 1] != 1)) {
							seat[j] = 2;
							break;
						}
					}
					isRightA = seat[j] == 1;
				}
			}
			else if (who == 'C') {
				for (int j = 0; j < n; ++j) {
					if (j != 0) {
						if (j != n - 1 && seat[j + 1] == 0) {
							seat[j + 1] = 2;
							break;
						}
						if (j != 0 && seat[j - 1] == 0) {
							seat[j - 1] = 2;
							break;
						}
					}
					if (j == n - 1)
						seat[n / 2] = 2;
				}
			}
			else if (who == 'D') {
				int maxDist = 334;
				int maxIdx = 0;

				int dist = 0;

				int fromTop = 0;
				int toLast = 0;

				for (int j = 0; j < n; ++j) {
					++dist;
					if (j == n - 1)
						toLast = dist;

					if (seat[j] != 0) {
						if (fromTop == 0)
							fromTop = j + 1;

						if (maxDist < dist / 2) {
							maxDist = dist / 2;
							maxIdx = j - dist;
						}
						dist = 0;
					}
				}

				if (seat[n - 1] == 0 && toLast > maxDist && fromTop < toLast)
					seat[n - 1] = 3;
				else if (seat[0] == 0 && fromTop > maxDist && fromTop > toLast)
					seat[0] = 3;
				else
					seat[maxIdx + maxDist] = 3;
			}
		}

		for (int i = 0; i < m; ++i)
			std::cout << output[i];
	}

	return 0;
}

C++: #include<iostream>
using namespace std;
int n,m;
char t[100],ch;
void putA();
void putB();
void putC();
void putD();
int main(){
  while(cin>>n>>m){
    if(n==0&&m==0)break;
    for(int i=0;i<n;i++)t[i]='#';
    for(int i=0;i<m;i++){
      cin>>ch;
      if(ch=='A')putA();
      else if(ch=='B')putB();
      else if(ch=='C')putC();
      else putD();
    }
    for(int i=0;i<n;i++)cout<<t[i];
    cout<<endl;
  }
  return 0;
}
void putA(){
  for(int i=0;i<n;i++){
    if(t[i]!='#')continue;
    t[i]='A';
    return;
  }
}
void putB(){
  for(int i=n-1;i>=0;i--){
    if(t[i]!='#')continue;
    if(i-1>=0&&t[i-1]=='A')continue;
    if(i+1<n&&t[i+1]=='A')continue;
    t[i]='B';
    return;
  }
  for(int i=0;i<n;i++){
    if(t[i]=='#'){
      t[i]='B';
      return;
    }
  }
}
void putC(){
  for(int i=0;i<n;i++){
    if(t[i]=='#')continue;
    if(i+1<n&&t[i+1]=='#'){
      t[i+1]='C';return;
    }else if(i-1>=0&&t[i-1]=='#'){
      t[i-1]='C';return;
    }
  }
  t[n/2]='C';
}
void putD(){
  bool flg=true;
  for(int i=0;i<n;i++)if(t[i]!='#')flg=false;
  if(flg){
    t[0]='D';return;
  }

  int l[100],r[100],m[100];
  l[0]=(t[0]=='#'?100:0);
  for(int i=1;i<n;i++){
    if(t[i]=='#')l[i]=l[i-1]+1;
    else l[i]=0;
  }
  r[n-1]=(t[n-1]=='#'?100:0);
  
  for(int i=n-2;i>=0;i--){
    if(t[i]=='#')r[i]=r[i+1]+1;
    else r[i]=0;
  }
  //for(int i=0;i<n;i++)cout<<t[i];cout<<endl;
  for(int i=0;i<n;i++){
    m[i]=min(l[i],r[i]);
    //cout<<m[i];
  }
  //cout<<endl;

  int pos=-1,maxm=0;
  for(int i=0;i<n;i++){
    if(t[i]!='#')continue;
    if(m[i]>maxm){
      pos=i;
      maxm=m[i];
    }
  }
  if(pos!=-1){
    t[pos]='D';
  }
}

C++: #include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<cstdio>
#include<sstream>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mp make_pair
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
const double EPS=1e-10;
const int inf=1e8;
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
int main(){
	int n,m;
	while(cin>>n>>m,n){
		vector<string>in(n,"");
//		rep(i,n)cin>>in[i];//
//		rep(i,n)if(in[i]=="0")in[i]="";
		rep(q,m){
			string s;cin>>s;
			if(s=="A"){
				rep(i,n)if(in[i]==""){
					in[i]="A";
					break;
				}
			}else if(s=="B"){
				vector<string>tmp=in;
				rep(i,n)if(in[i]=="A"){
					if(i)tmp[i-1]="!";
					if(i!=n-1)tmp[i+1]="!";
				}
				int I=inf;
				for(int i=n-1;i>=0;i--)if(tmp[i]==""){I=i;break;}
				if(I==inf){
					rep(i,n)if(in[i]==""){
						I=i;
						break;
					}
				}
				in[I]="B";
			}else if(s=="C"){
				if(!q){
					in[n/2]="C";
					continue;
				}
				rep(i,n)if(in[i]!=""){
					if(i!=n-1&&in[i+1]==""){
						in[i+1]="C";
						break;
					}else if(i&&in[i-1]==""){
						in[i-1]="C";
						break;
					}
				}
			}else{
				if(!q){
					in[0]="D";
					continue;
				}
				vi t;
				rep(i,n)if(in[i]!="")t.pb(i);
				int ma=t[0],mai=0;
				rep(i,t.size()-1){
					if(ma<(t[i+1]-t[i])/2){
						ma=(t[i+1]-t[i])/2;
						mai=t[i]+(t[i+1]-t[i])/2;
					}
				}
				if(ma<n-t[t.size()-1]-1){
					mai=n-1;
				}
				in[mai]="D";
			}
		}
		rep(i,n)cout<<(in[i]==""?"#":in[i]);
		cout<<endl;
	}
}