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 <bits/stdc++.h>
using namespace std;
int n,m;
char chair[200]={};

void A(char ch){
  int i=1;
  while(chair[i]!='#') i++;
  chair[i]=ch;
  assert(i<=n);
}

void B(){
  int i=n;
  while(chair[i]!='#')i--;
  chair[i]='B';
  assert(i>=0);
}

void C(int kai){
  if(kai==0){
    if(n%2)chair[(n+1)/2]='C';
    else chair[n/2+1]='C';
    return;
  }
  int f=1;
  for(int i=1;i<=n;i++){
    if(chair[i]=='#')continue;
    if(chair[i-1]=='#') chair[i-1]='C',i=n,f=0;
    if(chair[i+1]=='#') chair[i+1]='C',i=n,f=0;
  }
  assert(f);
}

void D(){
  int R=0,L=0;
  while(chair[n-R]=='#')R++;
  while(chair[L+1]=='#')L++;
  
  int M=0,idx=0,cnt=0;
  for(int i=1;i<=n;i++){
    if(chair[i]=='#')cnt++;
    else cnt=0;
    if(M+M%2<cnt) M=cnt,idx=i;
  }
  if(M<=2&&L<=1&&R<=1) A('D');
  else if(L-1>=(M-1)/2&&L-1>=R-1)chair[1]='D';
  else if(R-1>(M-1)/2)chair[n]='D';
  else chair[(idx-M+1)+(M-1)/2]='D';

}

int main(){
  while(1){
    cin>>n>>m;
    if(!n&&!m)break;
    memset(chair,'#',sizeof(chair));
    chair[0]=chair[n+1]=0;
    for(int i=0;i<m;i++){
      char a;
      cin>>a;
      if(a=='A') A(a);
      if(a=='B') B();
      if(a=='C') C(i);
      if(a=='D') D();
    }
    assert(strlen(chair+1)==n);
    printf("%s\n",chair+1);
  }
  return 0;
}

C++: #include<stdio.h>
int main(void)
{
    int n,m,i,j,flg,w,d,p,q,k,e[100];
	char s;
	while(1){
		scanf("%d %d",&n,&m);
		if(n==0&&m==0) break;
		for(i=0;i<n;i++) e[i]=0;
		for(i=0;i<m;i++){
			scanf(" %c",&s);
			if(s=='A'){
				for(j=0;j<n;j++){
					if(e[j]==0){
						e[j]=1; 
						break;
					}
				}
			}
			else if(s=='B'){
				flg=0;
				for(j=n-1;j>=0;j--){
					if(e[j]==0){
						if(e[j-1]!=1){
							e[j]=2;
							flg=1; break;
						}
					}
					else if(e[j]==1) j--;
				}
				if(flg==0){
					for(j=0;j<n;j++){
						if(e[j]==0){
							e[j]=2;
							break;
						}
					}
				}
			}
			else if(s=='C'){
				flg=0;
				if(i==0){
					e[n/2]=3;
				}
				else{
					for(j=1;j<n;j++){
						if(e[j-1]!=0&&e[j]==0) e[j]=3;flg=1; break;
					}
					if(flg==0){
						for(j=n-1;j>=0;j--){
							if(e[j]==0) e[j]=3;break;
						}
					}
				}
			}
			else if(s=='D'){
				flg=0;d=0; w=0;q=0;
				if(i==0){
					e[0]=4;
				}
				else {
					for(j=0;j<n;j++){
						if(e[j]==0) d++; flg=1;
						if(flg==1&&e[j]!=0){
							if(w<d){
								w=d;
								p=q;
								k=j-1;
							}
							d=0;
						}
						if(e[j]!=0) q=j;
					}
					e[p+w/2-1]=4;
				}
			}
		}
		for(i=0;i<n;i++){
			if(e[i]==0) printf("#");
			if(e[i]==1) printf("A");
			if(e[i]==2) printf("B");
			if(e[i]==3) printf("C");
			if(e[i]==4) printf("D");
		}
		printf("\n");
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <map>
#include <vector>
using namespace std;

char seat[110];
bool is_seat = false;
int n, m;

void A(){
  for(int i = 0 ; i < n ; i++){
    if(seat[i] == '#'){
      seat[i] = 'A';
      is_seat = true;
      return;
    }
  }
}

void B(){
  bool flag = false;
  for(int i = n-1 ; i >= 0 ; i--){
    if(seat[i-1] != 'A' && seat[i+1] != 'A' && seat[i] == '#'){
      seat[i] = 'B';
      flag = true;
      is_seat = true;
      return;
    }
  }
  if(!flag){
    for(int i = 0 ; i < n ; i++){
      if(seat[i] == '#'){
	seat[i] = 'B';
	is_seat = true;
	return;
      }
    }
  }
}

void C(){
  if(!is_seat){
    if(n % 2 == 1) seat[(n+1)/2-1] = 'C';
    else seat[n/2+1-1] = 'C';
    is_seat = true;
    return;
  }
  else{
    for(int i = 0 ; i < n ; i++){
      if(seat[i] != '#'){
	if(seat[i+1] == '#'){
	  seat[i+1] = 'C';
	  is_seat = true;
	  return;
	}
	else{
	  if(seat[i-1] == '#'){
	    seat[i-1] = 'C';
	    is_seat = true;
	    return;
	  }
	}
      }
    }
  }
}

void D(){
  bool Must_left = true;
  vector<pair<int, int> > check;
  if(!is_seat){
    is_seat = true;
    seat[0] = 'D';
    return;
  }
  
  for(int i = 0 ; i < n ; i++){
    if(seat[i-1] == '#' && seat[i+1] == '#') Must_left = false;
  }
  for(int i = 0 ; i < n ; i++){
    if(seat[i] == '#'){
      int cnt = 0;
      int len;
      for(int j = i-1 ; seat[j] == '#' || j >= 0; j--) cnt++;
      len = cnt; cnt = 0;
      for(int j = i+1 ; seat[j] == '#' || j < n ; j++) cnt++;
      len = max(len, cnt);
      check.push_back(make_pair(len, i));
    }
  }
  sort(check.begin(), check.end());
  for(int i = 0 ; i < check.size() ; i++){
    if(check[i].first == check[i+1].first) Must_left = true;
  }

  if(Must_left){
    for(int i = 0 ; i < n ; i++){
      if(seat[i] == '#'){
	seat[i] = 'D';
	is_seat = true;
	return;
      }
    }
  }
  else{
    seat[check[check.size()-1].second] = 'D';
    is_seat = true;
    return;
  }
}

int main(){
  while(cin >> n >> m){
    if(n == 0 && m == 0) break;
    fill(seat, seat+n, '#');
    char p;
    is_seat = false;
    while(m--){
      cin >> p;
      if(p == 'A') A();
      else if(p == 'B') B();
      else if(p == 'C') C();
      else if(p == 'D') D();
      /*for(int i = 0 ; i < n ; i++)cout << seat[i];
      cout << endl;*/
    }
    for(int i = 0 ; i < n ; i++)cout << seat[i];
    cout << endl;
  }
  return 0;
}