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 <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;
  }
  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]='#';
    for(int i=1;i<n;i++) cout <<t[i];
    cout <<t[n]<<endl;
  }
  return 0;
}

C++: #include<iostream>
using namespace std;
int n,m;
char t[100],ch;
void putA();
void putB();
void putC();
void putD();
int main(){
  while(cin>>n>>m){
    if(n==0&&m==0)break;
    for(int i=0;i<n;i++)t[i]='#';
    for(int i=0;i<m;i++){
      cin>>ch;
      if(ch=='A')putA();
      else if(ch=='B')putB();
      else if(ch=='C')putC();
      else putD();
    }
    for(int i=0;i<n;i++)cout<<t[i];
    cout<<endl;
  }
  return 0;
}
void putA(){
  for(int i=0;i<n;i++){
    if(t[i]!='#')continue;
    t[i]='A';
    return;
  }
}
void putB(){
  for(int i=n-1;i>=0;i--){
    if(t[i]!='#')continue;
    if(i-1>=0&&t[i-1]=='A')continue;
    if(i+1<n&&t[i+1]=='A')continue;
    t[i]='B';
    return;
  }
  for(int i=0;i<n;i++){
    if(t[i]=='#'){
      t[i]='B';
      return;
    }
  }
}
void putC(){
  for(int i=0;i<n;i++){
    if(t[i]=='#')continue;
    if(i+1<n&&t[i+1]=='#'){
      t[i+1]='C';return;
    }else if(i-1>=0&&t[i-1]=='#'){
      t[i-1]='C';return;
    }
  }
  t[n/2]='C';
}
void putD(){
  bool flg=true;
  for(int i=0;i<n;i++)if(t[i]!='#')flg=false;
  if(flg){
    t[0]='D';return;
  }

  int l[100],r[100],m[100];
  l[0]=999;
  for(int i=1;i<n;i++){
    if(t[i]=='#')l[i]=l[i-1]+1;
    else l[i]=0;
  }
  r[n-1]=999;
  for(int i=n-2;i>=0;i--){
    if(t[i]=='#')r[i]=r[i+1]+1;
    else r[i]=0;
  }
  for(int i=0;i<n;i++){
    m[i]=min(l[i],r[i]);
  }
  int pos=-1,mini=100;
  for(int i=0;i<n;i++){
    if(t[i]!='#')continue;
    if(m[i]<mini){
      pos=i;
      mini=m[i];
    }
  }
  if(pos!=-1){
    t[pos]='D';
  }
}

C++: #include <string>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
void solve1(string& s, char c) {
	s[s.find('#')] = c;
}
void solve2(string& s) {
	for (int i = s.size() - 1; i >= 0; i--) {
		if (!((i < s.size() - 1 && s[i + 1] == 'A') || (i > 0 && s[i - 1] == 'A'))) {
			s[i] = 'B'; return;
		}
	}
	solve1(s, 'B');
}
vector<int> dist(string& s) {
	vector<int> ret(s.size(), 999999999);
	for (int i = 0; i < s.size(); i++) {
		if (s[i] != '#') {
			for (int j = 0; j < s.size(); j++) {
				ret[j] = min(ret[j], abs(i - j));
			}
		}
	}
	return ret;
}
void solve3(string &s) {
	for (int i = 0; i < s.size(); i++) {
		if (s[i] != '#') {
			if (i < s.size() - 1 && s[i + 1] == '#') {
				s[i + 1] = 'C'; return;
			}
			if (i > 0 && s[i - 1] == '#') {
				s[i - 1] = 'C'; return;
			}
		}
	}
	if (s.size() % 2 == 1) s[(s.size() - 1) / 2] = 'C';
	else s[s.size() / 2] = 'C';
}
void solve4(string &s) {
	vector<int> ret = dist(s);
	s[max_element(ret.begin(), ret.end()) - ret.begin()] = 'D';
}
int N, Q;
int main() {
	while (cin >> N >> Q, N) {
		string s(N, '#'), t;
		while (Q--) {
			cin >> t;
			if (t == "A") solve1(s, 'A');
			if (t == "B") solve2(s);
			if (t == "C") solve3(s);
			if (t == "D") solve4(s);
		}
		cout << s << endl;
	}
	return 0;
}