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 <complex>
#include <sstream>
#include <string>
#include <algorithm>
#include <deque>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <vector>
#include <set>
#include <limits>
#include <cstdio>
#include <cctype>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
#define REP(i, j) for(int i = 0; i < (int)(j); ++i)
#define FOR(i, j, k) for(int i = (int)(j); i < (int)(k); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define REVERSE(v) reverse((v).begin(), (v).end())
typedef complex<double> P;

int N, M;

void check(vector<char> &v, char c){
  if(N == 1) { v[0] = c; return ; }
  if(c == 'A'){
    REP(i, v.size()) if(v[i] == '#'){ v[i] = c; return ; }
  }
  if(c == 'B'){
    if(v[N - 1] == '#' && v[N - 2] != 'A') { v[N - 1] = c; return ; }
    for(int i = N - 2; i > 1; i--) if(v[i] == '#' && v[i - 1] != 'A' && v[i + 1] != 'A') { v[i] = c; return ; }
    if(v[0] == '#' && v[1] != 'A') { v[0] = c; return ; }
    REP(i, v.size()) if(v[i] == '#'){ v[i] = c; return ; }
  }
  if(c == 'C'){
    if(v[0] != '#' && v[1] == '#') { v[1] = c; return ; }
    for(int i = 1; i < N - 1; i++){
      if(v[i] != '#' && v[i + 1] == '#') { v[i + 1] = c; return ; }
      if(v[i] != '#' && v[i - 1] == '#') { v[i - 1] = c; return ; }
    }
    if(v[N - 1] != '#' && v[N - 2] == '#') { v[N - 2] = c; return ; }
    if(N % 2) { v[(N + 1) / 2 - 1] = c; return ; }
    v[N / 2] = c;
  }
  if(c == 'D'){
    vector<int> d(N, 1e9);
    REP(i, N){
      if(v[i] == '#') continue;
      d[i] = 0;
      for(int j = i + 1, cnt = 1; j < N; ++j, ++cnt) d[j] = min(d[j], cnt);
      for(int j = i - 1, cnt = 1; j >= 0; --j, ++cnt) d[j] = min(d[j], cnt);
    }
    int tar = 0;
    REP(i, N) tar = max(tar, d[i]);
    if(tar == N) { v[0] = c; return ; }
    REP(i, N) if(d[i] == tar) { v[i] = c; return ; }
  }
}

int main() {
  while(cin >>N >>M && N && M){
    vector<char> v(N, '#');
    REP(i, M){
      char c; cin >>c;
      check(v, c);
    }
    REP(i, N) cout <<v[i]; cout <<endl;
  }
  return 0;
}

C++: #include <iostream>
using namespace std;
void solve(int n,int m){
	string s,a;
	int pos,temp,now;
	bool f,ok;
	for(int i=0;i<n;i++)s.push_back('#');
	for(int x=0;x<m;x++){
		cin>>a;
		if(a[0]=='A'){
			for(int i=0;i<n;i++)if(s[i]=='#'){
				s[i]='A';
				break;
			}
		}
		else if(a[0]=='B'){
			ok=false;
			for(int i=n-1;i>=0;i--)if(s[i]=='#'){
				f=true;
				if(i<n-1){
					if(s[i+1]=='A')f=false;
				}
				if(i>0){
					if(s[i-1]=='A')f=false;
				}
				if(f){
					s[i]='B';
					ok=true;
					break;
				}
			}
			if(!ok)for(int i=0;i<n;i++)if(s[i]=='#'){
				s[i]='B';
				break;
			}
		}
		else if(a[0]=='C'){
			if(x==0)s[n/2]='C';
			else{
				for(int i=0;i<n;i++)if(s[i]!='#'){
					if(i<n-1&&s[i+1]=='#'){
						s[i+1]='C';
						break;
					}
					else if(i>0&&s[i-1]=='#'){
						s[i-1]='C';
						break;
					}
				}
			}
		}
		else{
			if(x==0)s[0]='D';
			else{
				pos=temp=now=0;
				for(int i=0;i<n;i++){
					if(s[i]=='#'){
						temp=n;
						for(int j=i-1;j>=0;j--){
							if(s[j]!='#'){
								temp=i-j;
								break;
							}
						}
						for(int j=i+1;j<n;j++){
							if(s[j]!='#'){
								if(j-i<temp)temp=j-i;
								break;
							}
							
						}
						if(temp>now){
							now=temp;
							pos=i;
						}
					}
				}
				s[pos]='D';
			}
		}
	}
	cout<<s<<endl;
}
int main(){
	int n,m;
	while(true){
		cin>>n>>m;
		if(n==0&&m==0)break;
		solve(n,m);
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
int n,m;
char t[120];

void A(char a){
  int i=1;
  while(t[i]!=0) i++;
  t[i]=a;
}

void B(){
  for(int i=n;i>=1;i--){
    if(t[i]==0){
      t[i]='B';
      break;
    }
  }
}

void C(int cnt){
  if(cnt==0) {
    if(n%2==0) t[n/2+1]='C';
    else t[(n+1)/2]='C';
    return;
  }


  for(int i=1;i<=n;i++){
    if(t[i]!=0&&t[i+1]==0) {
      t[i+1]='C';
      break;
    }
    if(t[i]!=0&&t[i-1]==0){
      t[i-1]='C';
      break;
    }
  }
}

void D(int cnt){
  if(cnt==0){
    t[1]='D';
    return;
  }
  int mx=0,idx=0,c=0;
  for(int i=1;i<=n;i++) {
    if(t[i]==0) c++;
    else c=0;
    if(mx+mx%2<c)mx=c,idx=i;
  }
  cout <<c<<endl;

  if(mx<=2&&c==2&&mx<c) {
    t[n]='D';
    return;
  }  

  if(mx<=2){
    A('D');
    return ;
  }

  if(idx==n) t[n]='D';
  else   t[(idx-(idx-mx+1))/2+(idx-mx+1)]='D';
}

int main(){
  while(1){
    cin>>n>>m;
    if(!n&&!m)break;
    memset(t,0,sizeof(t));
    t[0]=t[n+1]=1;
    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);
    }

    for(int i=1;i<=n;i++)if(t[i]==0)t[i]='#';
    t[n+1]=0;
    printf("%s\n",t+1);
  }
  return 0;
}