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 <cstring>
#include <algorithm>

using namespace std;

int chair[100],pos,n,m;

int d(char c){
	if(c == 'A'){
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}else if(c == 'B'){
		for(int i=n-1;i>=0;i--){
			if(chair[i] == -1){
				if(i == 0){
					if(chair[i+1] != 'A') return i;
				}else if(i == n-1){
					if(chair[i-1] != 'A') return i;
				}else{
					if(chair[i-1] != 'A' && chair[i+1] != 'A') return i;
				}
			}
		}
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}else if(c == 'C'){
		for(int i=0;i<n;i++){
			if(chair[i] == -1){
				if(i+1 < n && chair[i+1] != -1) return i;
				if(0 <= i-1 && chair[i-1] != -1) return i;
			}
		}
		return n/2+1;
	}else{
		int d_min_max = 0,d_pos=-1,tmp;
		for(int i=0;i<n;i++){
			//ó¢Ä¢éÖqÆÅàß¢lÌ£ðßé
			
			if(chair[i] == -1){
				int dist_min = 1 << 28;
				if(i != n-1){
					tmp = 1;
					while(i+tmp < n && chair[i+tmp] == -1) tmp++;
					if(i+tmp<n){
						dist_min = min(dist_min, tmp);
					}
				}
				if(i != 0){
					tmp = 1;
					while(i-tmp >= 0 && chair[i-tmp] == -1) tmp++;
					if(i-tmp >= 0){
						dist_min = min(dist_min, tmp);
					}
				}
				if(d_min_max < dist_min){
					d_min_max = dist_min;
					d_pos = i;
				}
			}
		}
		if(d_pos != -1) return d_pos;
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}
}

int main(){
	while(cin >> n >> m){
		if(!(n|m)) break;
		char c;
		memset(chair, -1, sizeof(chair));
		for(int i=0;i<m;i++){
			cin >> c;
			chair[d(c)] = c;
		}
		for(int i=0;i<n;i++){
			if(chair[i] == -1){
				cout << "#";
			}else{
				cout << (char)chair[i];
			}
		}
		cout << endl;
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

int A(const string &s) {
  for(int i = 0; i < s.size(); ++i) {
    if(s[i] == '#') return i;
  }
  return -1;
}

int B(const string &s) {
  for(int i = s.size()-1; i >= 0; --i) {
    if(s[i] == '#') {
      bool a = i == 0 || s[i-1] != 'A';
      bool b = i+1 == s.size() || s[i+1] != 'A';
      if(a && b) return i;
    }
  }
  return A(s);
}

int C(const string &s) {
  for(int i = 0; i < s.size(); ++i) {
    if(s[i] != '#') {
      if(i+1 < s.size() && s[i+1] == '#') return i+1;
      if(i && s[i-1] == '#') return i-1;
    }
  }
  return s.size()/2;
}

int D(const string &s) {
  int maxi = -1, pos = -1;
  for(int i = 0, j = -1; i <= s.size(); ++i) {
    if(i == s.size() || s[i] != '#') {
      if(i-j-1 > maxi) {
        maxi = i-j-1;
        pos = j+1;
      }
      j = i;
    }
  }
  if(maxi == s.size()) return A(s);
  return pos + (maxi-1)/2;
}

int main() {
  for(int n, m; cin >> n >> m && (n|m);) {
    string s(n, '#');
    while(m--) {
      char c;
      cin >> c;
      int pos;
      switch(c) {
      case 'A': pos = A(s); break;
      case 'B': pos = B(s); break;
      case 'C': pos = C(s); break;
      case 'D': pos = D(s); break;
      }
      s[pos] = c;
    }
    cout << s << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <set>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,j) FOR(i,0,j)
#define mp std::make_pair

typedef long long ll;
typedef unsigned long long ull;
typedef std::pair<int,int> P;
typedef std::pair<int,P> State;

const int INF = 1001001001;

// S N E W(南北東西)
const int dx[8] = {0, 0, 1, -1, 1, 1, -1, -1}, dy[8] = {1, -1, 0, 0, 1, -1, 1, -1};

int N, M;
char chairs[100];

int main(){
    while(std::cin >> N >> M, N){
        REP(i, N){chairs[i] = '#';}

        REP(i, M){
            char c;
            std::cin >> c;

            if(c == 'A'){
                REP(j, N){
                    if(chairs[j] == '#'){chairs[j] = 'A'; break;}
                }
            }else if(c == 'B'){
                bool can = false;
                for(int j=N-1;j>=0;j--){
                    if(chairs[j] != '#'){continue;}
                    if(j-1 >= 0 && chairs[j-1] == 'A'){continue;}
                    if(j+1 < N && chairs[j+1] == 'A'){continue;}
                    chairs[j] = 'B';
                    can = true;
                    break;
                }
                if(can){continue;}
                REP(j, N){
                    if(chairs[j] == '#'){chairs[j] = 'B'; break;}
                }
            }else if(c == 'C'){
                if(i == 0){chairs[N/2] = 'C'; continue;}

                REP(j, N){
                    if(chairs[j] == '#'){continue;}
                    if(j+1 < N && chairs[j+1] == '#'){chairs[j+1] = 'C'; break;}
                    if(j-1 >= 0 && chairs[j-1] == '#'){chairs[j-1] = 'C'; break;}
                }
            }else if(c == 'D'){
                int pos = -1, max_l = 0;
                REP(j, N){
                    if(chairs[j] != '#'){continue;}

                    int l1 = INF, l2 = INF;
                    REP(k, j){
                        if(chairs[k] != '#'){l1 = j-k; break;}
                    }
                    for(int k=N-1;k>j;k--){
                        if(chairs[k] != '#'){l2 = k-j; break;}
                    }

                    if(std::min(l1, l2) > max_l){pos = j; max_l = std::min(l1, l2);}
                }

                chairs[pos] = 'D';
            }
        }

        REP(i, N){
            putchar(chairs[i]);
        }
        puts("");
    }
}