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 <vector>
#include <string.h>
using namespace std;

void sit_seat(char c, vector<char>& seat)
{
	if(c == 'A')
	{
		for(int i=0; i<seat.size(); i++)
		{
			if(seat[i] == 0)
			{
				seat[i] = c;
				break;
			}
		}
	}
	else if(c == 'B')
	{
		bool is_sit = false;
		for(int i=seat.size()-1; i>=0; i--)
		{
			if(seat[i] != 0) continue;

			int r = i+1;
			if(r>=0 && r<seat.size())
			{
				if(seat[r] == 'A') continue;
			}

			int l = i-1;
			if(l>=0 && l<seat.size())
			{
				if(seat[l] == 'A') continue;
			}

			seat[i] = c;
			is_sit = true;
			break;
		}

		if(!is_sit)
		{
			for(int i=0; i<seat.size(); i++)
			{
				if(seat[i] == 0) seat[i] = c;
			}
		}
	}
	else if(c == 'C')
	{
		bool is_sit = false;
		for(int i=0; i<seat.size(); i++)
		{
			if(seat[i] != 0) continue;
			int r = i+1;
			if(r>=0 && r<seat.size())
			{
				if(seat[r] != 0)
				{
					seat[i] = c;
					is_sit = true;
					break;
				}
			}

			int l = i-1;
			if(l>=0 && l<seat.size())
			{
				if(seat[l] != 0)
				{
					seat[i] = c;
					is_sit = true;
					break;
				}
			}
		}

		if(!is_sit)
		{
			if(seat.size() % 2 == 0)
			{
				seat[seat.size()/2] = c;
			}
			else
			{
				seat[(seat.size()-1)/2] = c;
			}
		}
	}
	else if(c == 'D')
	{
		bool is_people = false;
		for(int i=0; i<seat.size(); i++)
		{
			if(seat[i] != 0)
			{
				is_people = true;
				break;
			}
		}

		bool is_sit = false;
		if(!is_people)
		{
			seat[0] = c;
			is_sit = true;
		}

		if(!is_sit)
		{
			int mmd = 0;
			int p_sit = 0;
			for(int i=0; i<seat.size(); i++)
			{
				if(seat[i] != 0) continue;
				int r = i;
				while( 1 )
				{
					r++;
					if(r<0 || r>=seat.size())
					{
						r = 10000;
						break;
					}
					if(seat[r] != 0) break;
				}
				int rd = r - i;

				int l = i;
				while( 1 )
				{
					l--;
					if(l<0 || l>=seat.size())
					{
						l = -10000;
						break;
					}
					if(seat[l] != 0) break;
				}
				int ld = i - l;

				int d = min(rd, ld);
				if(mmd < d)
				{
					mmd = d;
					p_sit = i;
				}
			}
			
			seat[p_sit] = c;
		}
	}
	else
	{
		cout << "unknown nationality!" << endl;
		return;
	}
}

int main()
{
	int n, np;
	char c;
	while(cin >> n >> np, n|np)
	{
		vector<char> seat(n);
		memset(&seat[0], 0, sizeof(char)*n);

		for(int i=0; i<np; i++)
		{
			cin >> c;
			sit_seat(c, seat);
		}

		for(int i=0; i<n; i++)
		{
			if(seat[i] !=0) printf("%c", seat[i]);
			else printf("#");
		}
		printf("\n");
	}
}

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(i==n-1){if(s[i-1]!='A'&&s[i]=='#'){pp++,s[i]='B';break;}}
          else if(!i){if(s[i+1]!='A'&&s[i]=='#'){pp++,s[i]='B';break;}}
          else {if(s[i-1]!='A'&&s[i]=='#'&&s[i+1]!='A'){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!=n-1){if(s[i+1]=='#'){s[i+1]='C';pp++;break;}}
            if(i){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]='C';
        }
      }
      else if(p=="D"){
        int d[n]={},p=0,sp=0;
        for(int i=0;i<n;i++){

          int p1=0,p2=0;
          if(i==n-1)p1=100;
          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;
          p1=min(p1,p2);
          p=max(p,p1);
          d[i]=p1;
        }
        for(int i=0;i<n;i++)if(s[i]!='#')sp++;
        if(sp)s[0]='D';
        else for(int i=0;i<n;i++)
          if(d[i]==p){
            s[i]='D';
            break;
          }
      }

    }
    cout<<s<<endl;
  }
}