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
		}
		chairs := make([]string, n)
		for i := range chairs {
			chairs[i] = "#"
		}
		sit := func(who string) {
			if who == "A" {
				chairs[getStringIndex(chairs, "#")] = "A" // A国の人は左から見て行って空いている席を見つけ次第座る
				// log.Println(chairs)
			} else if who == "B" {
				f := true
				for i := n-1; i > -1; i-- {
					// B国の人はA国人の隣以外で、右端から空いている椅子に座る
					if chairs[i] == "#" && (i == 0 || chairs[i-1] != "A") && (i == n-1 || chairs[i+1] != "A") {
								chairs[i] = "B"
								f = false
								break
					}
				}
				// A国人の隣しか空いていない場合、我慢して左端から空いている椅子に座る
				if f {
					chairs[getStringIndex(chairs, "#")] = "B"
				}
				// log.Println(chairs)
			} else if who == "C" { // C国人は人の隣に座りたい
				for i := 0; i < n; i++ {
					if chairs[i] != "#" {
						if i + 1 <= n-1 && chairs[i+1] == "#" {
							chairs[i+1] = "C"
							break
						} else if i - 1 >= 0 && chairs[i-1] == "#" {
							chairs[i-1] = "C"
							break
						}
					}
				}
				// log.Println(chairs)
			} else { // who == "D"
				// D国の人は人から離れて座りたい
				// どうしても誰かの隣に座らなければならない場合、その中で一番左側にある椅子に座る
				scores := make([]int, n)
				for i := range scores {
					scores[i] = INF
				}
				for i, v := range chairs {
					if v == "#" {
						scores[i]++
					}
				}
				for i := n-1; i > -1; i-- {
					tmp := 0
					if chairs[i] == "#" {
						tmp++
					} else {
						tmp = 0
					}
					scores[i] = min(scores[i], tmp)
				}
				chairs[getIntIndex(scores, getMax(scores))] = "D"
				// log.Println(chairs)
			}
		}
		scanner.Scan()
		if first := scanner.Text(); first == "A" || first == "D" {
			chairs[0] = first
		} else if first == "B" {
			chairs[len(chairs)-1] = "B"
		} else {
			chairs[n/2] = "C"
		}
		// log.Println(chairs)
		for i := 0; i < m-1; i++ {
			scanner.Scan()
			sit(scanner.Text())
		}
		fmt.Println(strings.Join(chairs, ""))
	}
}

func getStringIndex(chairs []string, who string) int {
	for i, v := range chairs {
		if v == who {
			return i
		}
	}
	return -1
}

func getIntIndex(scores []int, target int) int {
	for i, v := range scores {
		if v == target {
			return i
		}
	}
	return -1
}

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

func getMax(scores []int) int {
	tmp := -1
	for _, v := range scores {
		if tmp < v {
			tmp = v
		}
	}
	return tmp
}

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;
	}
	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;
		}
	}
	if(bl[0].first==0&&bl[0].second==n){
		chair[0]=4;return;
	}else{
		int mi,mlen=-1;
		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=dis;mi=i;}
		}
		chair[bl[mi].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;
}

C++: #include<bits/stdc++.h>
using namespace std;
int main(){
  int n,m;
  while(cin>>n>>m,n){
    string s;
    for(int i=0;i<n;i++)s+='#';
    while(m--){
      string p;
      cin>>p;
      if(p=="A"){
        for(int i=0;i<n;i++)
          if(s[i]=='#'){
            s[i]='A';
            break;
          }
      }
      if(p=="B"){
        int pp=0;
        for(int i=n-1;i>0;i--)
          if(s[i-1]!='A'&&s[i]=='#'){pp++,s[i]='B';break;}
        if(!pp)for(int i=0;i<n;i++)
             if(s[i]=='#'){
               s[i]='B';
               break;
            }
      }
      if(p=="C"){
        int pp=0;
        for(int i=0;i<n;i++)
          if(s[i]!='#'){
            if(i){if(s[i-1]=='#'){s[i-1]='C';pp++;break;}}
            if(i!=n-1){if(s[i+1]=='#'){s[i+1]='C';pp++;break;}}
          }
        if(!pp){
          if(n%2)s[(n+1)/2-1]='C';
          else s[n/2-1]='C';
        }
      }
      else if(p=="D"){
        int d[n]={},p=0,sp=0;
        for(int i=0;i<n;i++){
          int p1=0,p2=0;
          for(int j=i;j<n;j++)
            if(s[j]=='#')p1++;
            else break;
          for(int j=i;j>=0;j--)
            if(s[j]=='#')p2++;
            else break;
            sp=max(max(p1,p2),sp);
          p1=min(p1,p2);
          p=max(p,p1);
          d[i]=p1;
        }
        if(sp==n)s[0]='D';
        else for(int i=0;i<n;i++)
          if(d[i]==p){
            s[i]='D';
            break;
          }
      }

    }
    cout<<s<<endl;
  }
}

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

int N;
int table[128];

void doA() {
  for(int i = 0; i < N; i++) if( table[i] == '#' ) {
      table[i] = 'A';
      return;
    }
}

void doB() {
  for(int i = N - 1; i >= 0; i--) {

    if( table[i] == '#' ) {
      
      bool a = false;
      if( i - 1 >= 0 && table[i - 1] == 'A' ) a = true;
      if( i + 1 < N && table[i + 1] == 'A' ) a = true;
      
      if( ! a ) {
        table[i] = 'B';
        return;
      }
    }    
  }

  for(int i = 0; i < N; i++) if( table[i] == '#' ) {
      table[i] = 'B';
      return;
    }

}

void doC() {
  for(int i = 0; i < N; i++) {
    if( table[i] != '#' ) {
      if( i + 1 < N && table[i + 1] == '#' ) {
        table[i + 1] = 'C'; return;
      }

      if( i - 1 < N && table[i - 1] == '#' ) {
        table[i - 1] = 'C'; return;
      }

    }
  }

  if( N & 1 ) table[(N + 1) / 2 - 1] = 'C';
  else table[N / 2] = 'C';
}

void doD() {
  static int temp[128];
  for(int i = 0; i < 128; i++) temp[i] = 987654321;
  
  for(int i = 0; i < N; i++) {
    if( table[i] != '#' ) 
      temp[i] = -1;
    else 
      for(int j = 0; j < N; j++) 
        if( table[j] != '#' ) {
          temp[i] = min( temp[i], abs(i - j));
        }
  }
  
  int best = 0;
  for(int i = 0; i < N; i++) 
    if( temp[best] < temp[i] )
      best = i;
  
  table[best] = 'D';
}

int main() {
  for(int M; cin >> N >> M, (N || M); ) {

    for(int i = 0; i < N; i++) table[i] = '#';

    for(int m = 0; m < M; m++) {
      char ch; cin >> ch;
      if( ch == 'A' ) doA();
      if( ch == 'B' ) doB();
      if( ch == 'C' ) doC();
      if( ch == 'D' ) doD();
    }
    for(int i = 0; i < N; i++) cout << (char)(table[i]); cout << endl;
  }
}