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
			}
		}
		fmt.Println(strings.Join(chair, ""))
	}
}

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 <set>
#include <vector>
#include <string>
#include <utility>
#include <algorithm>
#include <stdio.h>
using namespace std;
typedef pair<int,int> P;
int chair[110];
int n,m;
void A(){
	int ans=0;
	while(chair[ans]!=0)ans++;
	chair[ans]=1;
	return;
}
void B(){
	for(int i=n-1;i>=0;i--){
		if(chair[i]==0){
			if(i==0&&chair[1]!=1){chair[0]=2;return;}
			else if(i==n-1&&chair[n-2]!=1){chair[n-1]=2;return;}
			else if(0<i&&i<n-1&&chair[i-1]!=1&&chair[i+1]!=1){chair[i]=2;return;}
		}
	}
	int ans=0;
	while(chair[ans]!=0)ans++;
	chair[ans]=2;
	return;
}
void C(){
	int ans=0;
	if(chair[0]!=0){
		while(chair[ans]!=0)ans++;
		chair[ans]=3;
		return;
	}
	chair[n]=5;
	for(int i=0;i<n;i++){
		if(chair[i]!=0){
			if(chair[i+1]==0)chair[i+1]=3;
			else chair[i-1]=3;
			return;
		}
	}
	if(n%2)chair[(n+1)/2-1]=3;
	else chair[n/2]=3;
	return;
}
void D(){
	int a=0,f=0;
	P bl[52];
	bool in=false;
	for(int i=0;i<=n;i++){
		if(in&&chair[i]!=0){
			in=false;bl[a++]=P(f,i);
		}else if(!in&&chair[i]==0){
			in=true;f=i;
		}
	}
	//for(int i=0;i<a;i++)printf("bl[%d]:[%d,%d)\n",i,bl[i].first,bl[i].second);
	if(bl[0].first==0&&bl[0].second==n){
		chair[0]=4;return;
	}else{
		int m,mlen=0;
		for(int i=0;i<a;i++){
			int dis=(bl[i].second-bl[i].first-1)/2;
			if(bl[i].second==n)dis=bl[i].second-bl[i].first-1;
			if(dis>mlen){
				mlen=bl[i].second-bl[i].first;m=i;
			}
		}
		chair[(bl[m].first+mlen)%n]=4;return;
	}
}
int main()
{
	while(cin>>n>>m&&(n||m)){
		fill(chair,chair+n,0);
		chair[n]=5;
		while(m--){
			char c;cin>>c;
			if(c=='A')A();
			if(c=='B')B();
			if(c=='C')C();
			if(c=='D')D();
		}
		for(int i=0;i<n;i++){
			if(chair[i]==0)cout<<'#';
			if(chair[i]==1)cout<<'A';
			if(chair[i]==2)cout<<'B';
			if(chair[i]==3)cout<<'C';
			if(chair[i]==4)cout<<'D';
		}
		cout<<endl;
	}
    return 0;
}

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

void seatA(string& seats)
{
  for (string::iterator it(seats.begin()); it != seats.end(); ++it) {
    if (*it == '#') {
      *it = 'A';
      return;
    }
  }
}

void seatB(string& seats)
{
  string::reverse_iterator fallback = seats.rend();
  for (string::reverse_iterator it(seats.rbegin()); it != seats.rend(); ++it) {
    if (*it == '#') {
      // right
      if (it+1 != seats.rend() && *(it+1) != 'A') {
        *it = 'B';
        return;
      }
      // left
      if (it != seats.rbegin() && *(it-1) != 'A') {
        *it = 'B';
        return;
      }
      fallback = it;
    }
  }
  *fallback = 'B';
}

void seatC(string& seats)
{
  for (string::iterator it(seats.begin()); it != seats.end(); ++it) {
    if (*it != '#') {
      if (it != seats.end() && *(it+1) == '#') {
        *(it+1) = 'C';
        return;
      }
      if (it != seats.begin() && *(it-1) == '#') {
        *(it-1) = 'C';
      }
    }
  }
  seats[seats.size()/2] = 'C';
}

void seatD(string& seats)
{
  vector<int> tbl(seats.size(), 1000);
  for (string::size_type i = 0; i < seats.size(); i++) {
    if (seats[i] != '#') {
      for (vector<int>::size_type j = 0; j < tbl.size(); j++) {
        tbl[j] = min(tbl[j], abs(static_cast<int>(i - j)));
      }
    }
  }
  if (tbl.front() == 1000) {
    seats[0] = 'D';
  } else {
    string::size_type pos = 0;
    int m = -1;
    for (string::size_type i = 0; i < seats.size(); i++) {
      if (tbl[i] > m) {
        m = tbl[i];
        pos = i;
      }
    }
    seats[pos] = 'D';
  }
}

int main()
{
  int n, m;
  while (cin >> n >> m && n != 0) {
    string seats(n, '#');
    for (int i = 0; i < m; i++) {
      string s;
      cin >> s;
      if (s == "A") {
        seatA(seats);
      } else if (s == "B") {
        seatB(seats);
      } else if (s == "C") {
        seatC(seats);
      } else {
        seatD(seats);
      }
    }
    cout << seats << endl;
  }
  return 0;
}