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 <algorithm>
#define MAX 100

using namespace std;

int n,m;
char chair[MAX+1];

void A(){
  for(int i = 0 ; i < n ; i++){

    if(chair[i] == '#'){
      chair[i] = 'A';
      return;
    }

  }
}

void B(){
  int pos = -1;

  for(int i = 0 ; i < n ; i++){
    if(chair[i] == 'A'){
      pos = i;
    }
  }

  if(pos == -1){
    for(int i = n-1 ; i >= 0 ; i--){

      if(chair[i] == '#'){
	chair[i] = 'B';
	return;
      }

    }

  }
  else{
    for(int i = n-1 ; i > 0 ; i--){

      if(chair[i] == '#' && chair[i-1] != 'A'){
	chair[i] = 'B';
	return;
      }
    }

    for(int i = 0 ; i < n ; i++){

      if(chair[i] == '#'){
	chair[i] = 'B';
	return;
      }

    }
  }

}

void C(){
  int cnt = count(chair,chair+n,'#');

  if(cnt == n){
    if(n % 2){
      chair[(n+1)/2] = 'C';
    }
    else{
      chair[n/2+1] = 'C';
    }
    return;
  }
  else{
    for(int i = 0 ; i < n ; i++){

      if(chair[i] != '#'){

	if(i != n-1 && chair[i+1] == '#'){
	  chair[i+1] = 'C';
	  return;
	}
	else{

	  if(i && chair[i-1] == '#'){
	    chair[i-1] = 'C';
	    return;
	  }

	}

      }

    }
  }

}

void D(){
  int Breadth = 0,pos;

  for(int i = 0 ; i < n ; i++){
    if(chair[i] !='#') continue;

    int dist = (1<<29);
    for(int j = 0 ; j < n ; j++){
      if(chair[j] != '#'){
	dist = min(dist,abs(i-j));
      }
    }
    if(Breadth < dist){
      Breadth = dist;
      pos = i;
    } 
  }

  chair[pos] = 'D';
}

int main(){
  while(cin >> n >> m , n | m){
    char person;

    for(int i = 0 ; i < n ; i++)
      chair[i] = '#';

    for(int i = 0 ; i < m ; i++){
      cin >> person;
     
      switch(person){
      case 'A':	
	A(); 
	break;
      case 'B': 
	B(); 
	break;
      case 'C': 
	C(); 
	break;
      case 'D': 
	D(); 
	break;
      }

    }

    for(int i = 0 ; i < n ; i++){
      cout << chair[i];
    }
    cout << endl;
  }

  return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
void A(vector<char>&);
void B(vector<char>&);
void C(vector<char>&);
void D(vector<char>&);
char get(vector<char>&, bool, int);
int main() {
	int n, m;
	while (cin >> n >> m&&n != 0) {
		vector<char> line(n + 1, '#');
		for (int i = 0; i < m; ++i) {
			char num;
			cin >> num;
			if (num == 'A') {
				A(line);
			}
			else if (num == 'B') {
				B(line);
			}
			else if (num == 'C') {
				C(line);
			}else{
				D(line);
			}
		}
		for (int i = 1; i < line.size(); ++i) {
			cout << line[i];
		}
		cout << endl;
	}
	return 0;
}

char get(vector<char>&line, bool right, int place) {
	if (right) {
		if (place == line.size() - 1)return '#';
		else return line[place + 1];
	}
	else {
		return line[place - 1];
	}
}

void A(vector<char> &line) {
	for (int i = 1; i < line.size(); ++i) {
		if (line[i] == '#') {
			line[i] = 'A';
			break;
		}
	}
}

void B(vector<char> &line) {
	for (int i = line.size() - 1; i > 0; --i) {
		if (line[i] == '#'&&get(line, true, i) != 'A' && get(line, false, i) != 'A') {
			line[i] = 'B';
			return;
		}
	}
	for (int i = 1; i < line.size(); ++i) {
		if (line[i] == '#') {
			line[i] = 'B';
			return;
		}
	}
}

void C(vector<char> &line) {
	for (int i = 1; i < line.size(); ++i) {
		if (line[i] != '#') {
			if (i != line.size() - 1 && line[i + 1] == '#') {
				line[i + 1] = 'C';
				return;
			}
			else if (i != 1 && line[i - 1] == '#') {
				line[i - 1] = 'C';
				return;
			}
		}
	}
	if (line.size() % 2 == 0) {
		line[line.size() / 2] = 'C';
		return;
	}
	else {
		line[line.size() / 2 + 1] = 'C';
	}
}

void D(vector<char> &line) {
	vector<int> dline(line.size());
	int num = line.size() + 1;
	bool flag = false;
	for (int i = 1; i < line.size(); ++i) {
		++num;
		if (line[i] != '#') {
			num = 0;
			flag = true;
		}
		dline[i] = num;
	}
	if (!flag) {
		line[1] = 'D';
		return;
	}
	num = line.size() + 1;
	for (int i = line.size() - 1; i > 0; --i) {
		++num;
		if (line[i] != '#') {
			num = 0;
		}
		dline[i] = min(dline[i], num);
	}
	int mn = 0, mp = 0;
	for (int i = 1; i < line.size(); ++i) {
		if (mn < dline[i]) {
			mn = dline[i];
			mp = i;
		}
	}
	line[mp] = 'D';
}

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();
    }
    int cnt=0;
    for(int i=1;i<=n;i++) if(chair[i]!='#') cnt++;
    assert(cnt==m);
    printf("%s\n",chair+1);
  }
  return 0;
}