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<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) REP((i),0,(n))
#define RREP(i,a,b) for(int i=(int)(a);i>=(int)(b);i--)
#define rrep(i,n) RREP(i,n,0)
#define each(it,X) for(__typeof((X).begin())  it=(X).begin();it!=(X).end();it++)
#define all(v) ((v).begin(),(v).end())
#define fi first
#define se second
#define pb push_back
typedef pair<int,int>pr;
typedef vector<int>vi;
typedef vector<vi>vvi;
typedef set<int>si;
const int INF=1070000000ll;
const int mod=1000000007ll;

int n,m;
char seet[100];
void A(){
    rep(i,n)if(seet[i]=='#'){
        seet[i]='A';
        return;
    }
}
void B(){
    rrep(i,n-1)if(seet[i]=='#'){
        if((i!=0||seet[i-1]!='A')&&(i!=n-1||seet[i+1]!='A')){
            seet[i]='B';
            return;
        }
    }
    rep(i,n)if(seet[i]=='#'){
        seet[i]='B';
        return;
    }
}
void C(){
    rep(i,n)if(seet[i]=='#'){
        if((i!=0&&seet[i-1]!='#')||(i!=n-1&&seet[i+1]!='#')){
            seet[i]='C';
            return;
        }
    }
    seet[n/2]='C';
}
void D(){
    int ma=0,dist=0;
    rep(i,n)if(seet[i]=='#'){
        int v=1000;
        rep(j,n)if(seet[j]!='#'){
            v=min(abs(i-j),v);
        }
        if(dist<v){
            dist=v;
            ma=i;
        }
    }
    seet[ma]='D';
}
signed main(){
    cin.tie(0);ios_base::sync_with_stdio(0);

    while(cin>>n>>m,n||m){
        fill_n(seet,n,'#');
        rep(i,m){
            char c;cin>>c;
            switch(c){
                case 'A':A();break;
                case 'B':B();break;
                case 'C':C();break;
                case 'D':D();break;
            }
        }
        rep(i,n)cout<<seet[i];cout<<endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

int A(const string &s) {
  for(int i = 0; i < s.size(); ++i) {
    if(s[i] == '#') return i;
  }
  return -1;
}

int B(const string &s) {
  for(int i = s.size()-1; i >= 0; --i) {
    if(s[i] == '#') {
      bool a = i == 0 || s[i-1] != 'A';
      bool b = i+1 == s.size() || s[i+1] != 'A';
      if(a && b) return i;
    }
  }
  return A(s);
}

int C(const string &s) {
  for(int i = 0; i < s.size(); ++i) {
    if(s[i] != '#') {
      if(i+1 < s.size() && s[i+1] == '#') return i+1;
      if(i && s[i-1] == '#') return i-1;
    }
  }
  return s.size()/2;
}

int D(const string &s) {
  int maxi = -1, pos = -1;
  for(int i = 0, j = -1; i <= s.size(); ++i) {
    if(i == s.size() || s[i] != '#') {
      if(i-j-1 > maxi) {
        maxi = i-j-1;
        pos = j+1;
      }
      j = i;
    }
  }
  if(maxi == s.size()) return A(s);
  if(pos + maxi == s.size()) return pos + maxi/2;
  return pos + (maxi-1)/2;
}

int main() {
  for(int n, m; cin >> n >> m && (n|m);) {
    string s(n, '#');
    while(m--) {
      char c;
      cin >> c;
      int pos;
      switch(c) {
      case 'A': pos = A(s); break;
      case 'B': pos = B(s); break;
      case 'C': pos = C(s); break;
      case 'D': pos = D(s); break;
      }
      s[pos] = c;
    }
    cout << s << endl;
  }
  return 0;
}

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 i=0;
  for(i=1;i<=n;i++){
    if(chair[i]=='#')continue;
    if(chair[i+1]=='#') chair[i+1]='C',i=n+1;
    else if(chair[i-1]=='#') chair[i-1]='C',i=n+1;
   
  }
    assert(i!=n+2);
}

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;
}