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 <string>
using namespace std;
#define MAX 100
int main(){
	int seat,people;
	while(cin>>seat>>people){
		if(seat+people==0 )break;
		string str[101],x;
		for( int i=0 ; i<=MAX ; i++ )
			str[i]="#";
		for( int i=0 ; i<people ; i++ ){
			cin>>x;
			if(x=="A"){
				for( int j=0 ; j<seat ; j++ ){
					if(str[j]=="#"){
						str[j]="A";
						break;
					}
				}
			}

			else if(x=="B"){
				int all_b_sign=0;
				for(int j=seat-1 ; j>=0 ; j-- ){
					if(str[j]=="#"){
						int B_sign=0;
						if(j==0)
							B_sign=1;
						else if(j==seat-1)
							if(str[j-1]!="A")
								B_sign=1;
						else if(str[j+1]!="A"&&str[j-1]!="A")
							B_sign=1;
						if(B_sign==1){
							str[j]="B";
							all_b_sign=1;
							break;
						}
					}
				}
				if(all_b_sign==0){
					for(int j=0 ; j<seat ; j++ ){
						if(str[j]=="#"){
							str[j]="B";
							break;
						}
					}
				}
			}

			else if(x=="C"){
				int c_sign=0;
				for(int j=0 ; j<seat ; j++ ){
					if(str[j]!="#"){
						if(j==seat-1){
							if(str[j-1]=="#"){
								str[j-1]="C";
								c_sign=1;
								break;
							}
						}
						else if(j==0){
							if(str[j+1]=="#"){
								str[j+1]="C";
								c_sign=1;
								break;
							}
						}
						else if(str[j+1]=="#"){
							str[j+1]="C";
							c_sign=1;
							break;
						}
						else if(str[j-1]=="#"){
							str[j-1]="C";
							c_sign=1;
							break;
						}

					}
				}
				if(c_sign==0){
					if(seat%2)
						str[(seat+1)/2]="C";
					else
						str[seat/(2+1)]="C";
				}
			}

			else if(x=="D"){
				if(i==0){
					str[0]="D";
					continue;
				}
				int location,max=0;
				for( int j=seat-1 ; j>=0 ; j-- ){
					int l=j;
					while(l>0){
						if(str[l]!="#"){
							if(max<=j-l){
								max=j-l;
								location=j;
							}
							break;
						}
						l--;
					}
					l=j;
					while(l<seat){
						if(str[l]!="#"){
							if(max<=l-j){
								max=l-j;
								location=j;
							}
							break;
						}
						l++;
					}
				}
				str[location]="D";
			}

		}
		for(int i=0 ; i<seat ; i++ )
			cout<<str[i];
		cout<<endl;
	}
}

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;
}

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

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

void D(int kai){
  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');
    return;
  }
   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(i);
    }
    assert(chair[n+1]==0);
    printf("%s\n",chair+1);
  }
  return 0;
}

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;
}

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

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;
    else 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()
{
	int n,m,i,j,k;
	char c;
	while(scanf("%d%d",&n,&m),n)
	{
		int a[100]={0};
		for(k=0;k<m;++k)
		{
			scanf(" %c",&c);
			if(c=='A')
			{
				for(i=0;i<n;++i)if(!a[i]){a[i]=1;break;}
			}
			if(c=='B')
			{
				for(i=n-1;i>=0;--i)if(!a[i]){a[i]=2;break;}
			}
			if(c=='C')
			{
				if(!k)a[n/2]=3;
				else
				{
					for(i=0;i<n;++i)
					{
						if(i!=n-1&&a[i]&&!a[i+1]){a[i+1]=3;break;}
						if(i&&a[i]&&!a[i-1]){a[i-1]=3;break;}
					}
				}
			}
			if(c=='D')
			{
				if(!k)a[0]=4;
				else
				{
					int mc=-1,mi=-1,x,y;
					for(i=0;i<n;++i)
					{
						x=y=999;
						for(j=i;j>=0;--j)if(a[j]){x=i-j;break;}
						for(j=i;j<n;++j)if(a[j]){y=j-i;break;}
						if(x>y)x=y;
						if(mc<x)mc=x,mi=i;
					}
					a[mi]=4;
				}
			}
		}
		for(i=0;i<n;++i)putchar("#ABCD"[a[i]]);
		puts("");
	}
	return 0;
}