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[:len(chair)-1], ""))
	}
}

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++: // Tazoe

#include <iostream>
using namespace std;

int main()
{
	while(true){
		int n, m;
		cin >> n >> m;

		if(n==0&&m==0)
			break;

		char C[10000];
		for(int i=0; i<n; i++){
			C[i] = '#';
		}

		for(int i=0; i<m; i++){
			char a;
			cin >> a;

			if(a=='A'){
				for(int j=0; j<n; j++){
					if(C[j]=='#'){
						C[j] = a;
						break;
					}
				}
			}
			else if(a=='B'){
				bool flg = false;
				for(int j=n-1; j>=0; j--){
					if(C[j]=='#'&&(j==0||C[j-1]!='A')&&(j==n-1||C[j+1]!='A')){
						C[j] = a;
						flg = true;
						break;
					}
				}

				if(!flg){
					for(int j=0; j<n; j++){
						if(C[j]=='#'){
							C[j] = a;
							break;
						}
					}
				}
			}
			else if(a=='C'){
				if(i==0){
					C[n/2] = a;
				}
				else{
					for(int j=0; j<n; j++){
						if(C[j]!='#'&&j!=n-1&&C[j+1]=='#'){
							C[j+1] = a;
							break;
						}
						else if(C[j]!='#'&&j!=0&&C[j-1]=='#'){
							C[j-1] = a;
							break;
						}
					}
				}
			}
			else if(a=='D'){
				if(i==0){
					C[0] = a;
				}
				else{
					int D[10000];
					int d = 10000;
					for(int j=0; j<n; j++){
						if(C[j]!='#'){
							d = 0;
							D[j] = d;
						}
						else{
							d++;
							D[j] = d;
						}
					}

					d = 10000;
					for(int j=n-1; j>=0; j--){
						if(C[j]!='#'){
							d = 0;
						}
						else{
							d++;
							if(D[j]>d){
								D[j] = d;
							}
						}
					}

					int d_max = -1;
					int j_max = -1;
					for(int j=0; j<n; j++){
						if(D[j]>d_max){
							d_max = D[j];
							j_max = j;
						}
					}

					C[j_max] = a;
				}
			}
		}

		for(int i=0; i<n; i++){
			cout << C[i];
		}
		cout << '\n';
	}

	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>

using namespace std;

#define rep(i,j) REP((i), 0, (j))
#define REP(i,j,k) for(int i=(j);(i)<(k);++i)
#define BW(a,x,b) ((a)<=(x)&&(x)<=(b))
#define F first
#define S second
#define INF 1 << 30

typedef pair<int, int> pi;
typedef pair<int, pi> pii;
typedef vector<int> vi;
typedef queue<int> qi;
typedef long long ll;

int n, m, f, dis, pos;
char c[100];

int main(){
  while(scanf("%d%d", &n, &m) && n){
    rep(i, n) c[i] = '#';
    char p[2];
    rep(k, m){
      scanf("%s", p);
      switch(p[0]){
      case 'A':
	rep(i, n) if(c[i] == '#'){ c[i] = 'A'; break;;}
	break;
      case 'B':
	if(c[n-2] != 'A' && c[n-1] == '#'){ c[n-1] = 'B'; break;}
	for(int i = n-2; i > 0; i--) if(c[i+1] != 'A' && c[i-1] != 'A' && c[i] == '#'){ c[i] = 'B'; goto e1;}
	if(c[1] != 'A' && c[0] == '#'){ c[0] = 'B'; break;}
	rep(i, n) if(c[i] == '#'){ c[i] = 'B'; break;}
      e1:
	break;
      case 'C':
	rep(i, n) if(c[i] != '#'){
	  if(i+1 < n && c[i+1] == '#'){ c[i+1] = 'C'; goto e2;}
	  else if(i-1 >= 0 && c[i-1] == '#'){ c[i+1] = 'C'; goto e2;}
	}

	if(n%2) c[(n+1)/2-1] = 'C';
	else c[n/2] = 'C';
      e2:
	break;
      case 'D':
	dis = 0, pos = 0;
	rep(i, n){
	  if(c[i] != '#') continue;
	  int j;
	  f = 0;
	  for(j = 1; j < n; j++){
	    if(i-j >= 0 && c[i-j] != '#') f = 1;
	    //	    printf("%d ", f);
	    if(i+j < n && c[i+j] != '#') f = 1;
	    //	    printf("%d ", f);
	    if(f){
	      if(dis < j){
		dis = j;
		pos = i;
	      }
	      break;
	    }
	  }
	  //	  printf("%d %d %d\n",i, dis, pos);
	}

	c[pos] = 'D';
	break;
      }
    }
  
    rep(i, n) putchar(c[i]); puts("");
  }
  return 0;
}

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<c) mx=c,idx=n;
  if(mx<=2&&t[n]==0&&t[n-1]==0) {
    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;
}