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
		}
		chair := make([]string, n+1)
		for i := range chair {
			chair[i] = "#"
		}
		chair[n] = "Sentinel"
		for i := 0; i < m; i++ {
			scanner.Scan()
			switch who := scanner.Text(); who {
			case "A": // 左から眺めて行って空いている席があったら即座に座る
				for j := 0; j < n; j++ {
					if chair[j] == "#" {
						chair[j] = "A"
						break
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "B":
				flag := true
				// 右端からAの隣でない席を探していく
				for j := n-1; j > -1; j-- {
					if chair[j] == "#" && (j == 0 || chair[j-1] != "A") && chair[j+1] != "A" {
						flag = false
						chair[j] = "B"
						break
					}
				}
				// Aの隣しか空いていないので一番左端の空いている席に座る
				if flag {
					for j := 0; j < n; j++ {
						if chair[j] == "#" {
							chair[j] = "B"
							break
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "C":
				if i == 0 {
					chair[n/2] = "C" // 先客が誰もいないときは真ん中の椅子に座る
				} else {
					for j := 0; j < n; j++ { // 左から舐めて
						if chair[j] != "#" { // その席が空いていなくて
							if chair[j+1] == "#" { // 右隣が空いているなら座る
								chair[j+1] = "C"
								break
							} else if j != 0 && chair[j-1] == "#" { // 右隣が空いていないので左隣に座る
								chair[j-1] = "C"
								break
							}
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "D":
				distanceTable := make([]int ,n)
				for j := range distanceTable {
					distanceTable[j] = INF
				}
				for j:= 0; j < n; j++ {
					if chair[j] != "#" {
						for k := 0; k < n; k++ {
							distanceTable[k] = min(distanceTable[k], abs(j-k))
						}
					}
				}
				// log.Println("distanceTAble:", distanceTable)
				at := 0
				distance := 0
				for j := 0; j < n; j++ {
					if distance < distanceTable[j] {
						at = j
						distance = distanceTable[j]
					}
				}
				chair[at] = "D"
				// log.Println(chair)
				break // 次の人を読み込む
			}
		}
		for i := 0; i < n; i++ {
			if i == n-1 {
				fmt.Println(chair[i])
			} else {
				fmt.Printf("%s ", chair[i])
			}
		}
	}
}

func min(a, b int) int {
	if a > b {
		return b
	}
	return a
}

func abs(a int) int {
	if a < 0 {
		return -a
	}
	return a
}

C++: #include <iostream>
#include <algorithm>

#define MAX 100

using namespace std;

int n,m;
char chair[MAX+2];
 
void A(){
  for(int i = 1 ; i <= n ; i++){
    if(chair[i] == '#'){
      chair[i] = 'A';
      return;
    }
  }
}

void B(){
  int pos = -1;
  
  for(int i = 1 ; i <= n ; i++){
    if(chair[i] == 'A'){
      pos = i;
      break;
    }
  }
  
  if(pos == -1){
    for(int i = n ; i > 0 ; i--){
      if(chair[i] == '#'){
        chair[i] = 'B';
        return;
      } 
    }
  }
  else{
    for(int i = n ; i > 0 ; i--){
      if(chair[i] == '#' && chair[i-1] != 'A' && chair[i+1] != 'A'){
	chair[i] = 'B';
	return;
      }
    }
 
    for(int i = 1 ; 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';
    }
  }
  else{
    for(int i = 1 ; i <= n ; i++){
      if(chair[i] != '#' && chair[i+1] == '#' && i != n){
        chair[i+1] = 'C';
        return;
      }
      if(chair[i] != '#' && chair[i-1] == '#' && i != 1){
        chair[i-1] = 'C';
        return;
      }
    }
  }
}
 
void D(){
  int Breadth = 0, pos;
  int cnt = count(chair,chair+n,'#');

  if(cnt == n){
    chair[1] = 'D';
    return;
  } 

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

C++: #include <iostream>
#include <cstring>
using namespace std;

#define REP(i,n,m) for(int i=n;i<m;i++)
#define rep(i,n) REP(i,0,n)

int n;
char s[104];

int A(void){
	rep(i,n) if(s[i] == '#') return i;
	return -1;
}

int B(void){
	for(int i=n-1;i>=0;i--){
		if(s[i] == '#'){
			int l = i - 1;
			int r = i + 1;
			if(l >= 0 && s[l] == 'A') continue;
			if(r < n && s[r] == 'A') continue;

			return i;
		}
	}

	return -1;
}

int C(void){
	rep(i,n){
		if(s[i] != '#'){
			int l = i - 1;
			int r = i + 1;
			if(l >= 0 && s[l] == '#') return l;
			if(r < n && s[r] == '#') return r;
		}
	}

	return -1;
}

int D(void){
	int res = -1;
	int maxDist = 0;

	rep(i,n){
		if(s[i] == '#'){
			int ldist;
			int rdist;

			for(ldist=i-1;ldist>=0 && s[ldist]=='#';ldist--);
			for(rdist=i+1;rdist<n && s[rdist]=='#';rdist++);

			if(ldist < 0) ldist = i;
			if(rdist >= n) rdist = i;

			ldist = i - ldist;
			rdist = rdist - i;

			if(maxDist < min(ldist==0?999:ldist,rdist==0?999:rdist)){
				res = i;
				maxDist = min(ldist==0?999:ldist,rdist==0?999:rdist);
			}
		}
	}

	return res;
}

int main(void){
	int m;

	while(cin>>n>>m && (n||m)){
		memset(s,'#',sizeof(s));

		rep(i,m){
			int idx;
			char ch;
			cin>>ch;

			switch(ch){
			case 'A':
				s[A()] = 'A';
				break;
			case 'B':
				idx = B();
				s[(idx == -1 ? A() : idx)] = 'B';
				break;
			case 'C':
				idx = C();
				s[(idx == -1 ? n/2 : idx)] = 'C';
				break;
			case 'D':
				s[(i == 0 ? 0 : D())] = 'D';
				break;
			}
		}

		rep(i,n) cout<<s[i];
		cout<<endl;
	}

	return 0;
}

C++: #include<iostream>

char *chr, *peo;
int n,m;

void sitA(int i){
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'A';
			return;
		}
	}
}

void sitB(int i){
	if(chr[n-1] == '#' && chr[n-2] != 'A'){
		chr[n-1] = 'B';
		return;
	}
	for(int k=n-2; k>0; k--){
		if(chr[k] == '#' && chr[k-1] != 'A' && chr[k+1] != 'A'){
			chr[k] = 'B';
			return;
		}
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'B';
			return;
		}
	}
}

void sitC(int i){
	if(i==0){
		if(n%2 == 0)
			chr[n/2] = 'C';
		else
			chr[(n-1)/2] = 'C';
		return;
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#')
			continue;
		if(k<n-1){
			if(chr[k+1] == '#'){
				chr[k+1] = 'C';
				return;
			}
		}
		if(k>0){
			if(chr[k-1] == '#'){
				chr[k-1] = 'C';
				return;
			}
		}
	}
}

void sitD(int i){
	if(i==0){
		chr[0] = 'D';
		return;
	}
	int ans,tmp=0,tmp1,tmp2;
	for(int k=0; k<n; k++){
		if(chr[k] != '#')
			continue;
		tmp1=0;
		tmp2=0;
		for(int t=k; t<n; t++){
			if(chr[t] != '#')
				break;
			tmp1++;
			if(t == n-1)
				tmp1 = n+1;
		}
		if(k == n-1)
			tmp1 = n+1;
		for(int t=k; t>=0; t--){
			if(chr[t] != '#')
				break;
			tmp2++;
			if(t == 0)
				tmp2 = n+1;
		}
		if(k == 0)
			tmp2 = n+1;
		if(tmp1 > tmp2)
			tmp1 = tmp2;
		if(tmp1 > tmp){
			tmp = tmp1;
			ans = k;
		}
	}
	chr[ans] = 'D';
}

void solve(){
	char tmp;
	for(int i=0; i<m; i++){
		tmp = peo[i];
		switch(tmp){
		case 'a':
		case 'A':
			sitA(i);
			break;
		case 'b':
		case 'B':
			sitB(i);
			break;
		case 'c':
		case 'C':
			sitC(i);
			break;
		case 'd':
		case 'D':
			sitD(i);
			break;
		}
	}
	std::cout << chr << std::endl;
}

int main(){
	while(true){
		std::cin >> n >> m;
		if(!n && !m)
			return 0;
		chr = new char[n];
		peo = new char[m];
		for(int i=0; i<n; i++){
			chr[i] = '#';
			if(i<m)
				std::cin >> peo[i];
		}
		solve();
		delete[] chr;
		delete[] peo;
	}
}