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 <cstdio>
#include <algorithm>
#include <vector>
#include <string>
#include <numeric>
#include <stdio.h>

using namespace std;

const int inf = 1e9 + 7;

int main() {

	while (1) {
		int n, m;
		cin >> n >> m;
		if (n == 0 && m == 0) break;
		vector<char> a(m);
		for (int i = 0; i < m; i++) cin >> a[i];

		vector<int> dis(n, inf);
		// 順にやってけばいいのかな
		vector<char> ans(n, '#');
		for (int i = 0; i < m; i++) {
			if (a[i] == 'A') {
				// 左から座る
				for (int j = 0; j < n; j++) {
					if (ans[j] == '#') {
						ans[j] = a[i];
						break;
					}
				}
			}
			else if (a[i] == 'B') {
				// 右から座る
				bool ok = false;
				for (int j = n - 1; j >= 0; j--) {
					if (ans[j] == '#') {
						// 隣がA国人か
						if (j + 1 < n) if (ans[j + 1] == 'A')continue;
						if (j - 1 >= 0) if (ans[j - 1] == 'A') continue;
						ans[j] = a[i];
						ok = true;
						break;
					}
				}
				if (!ok) { // まだ座れてなかったら
					for (int j = 0; j < n; j++) {
						if (ans[j] == '#') {
							ans[j] = a[i];
							break;
						}
					}
				}
			}
			else if (a[i] == 'C') {
				if (i == 0) {
					// 始めの人
					if (n % 2 == 1) ans[(n + 1) / 2 - 1] = a[i];
					else ans[n / 2] = a[i];
					continue;
				}
					// 左から人がいるかみてく
				for (int j = 0; j < n; j++) {
					if (ans[j] != '#') {
						bool ok = false;
						if (j + 1 < n) {
							if (ans[j + 1] == '#') {
								ans[j + 1] = a[i];
								ok = true;
								break;
							}
						}
						if (j - 1 >= 0) {
							if (ans[j - 1] == '#') {
								ans[j - 1] = a[i];
								ok = true;
								break;
							}
						}
						if (!ok) continue;
					}
				}
			}
			else if (a[i] == 'D') {
				if (i == 0) {
					ans[0] = a[i];
					continue;
				}
				// 一番近い人との距離をそれぞれ求める
				// 左右両方から調べる
				int cnt = inf - n;
				for (int j = 0; j < n; j++) {
					if (ans[j] != '#') {
						dis[j] = 0;
						cnt = 0;
					}
					else {
						dis[j] = ++cnt;
					}
				}
				// 反対からも
				for (int j = n - 1; j >= 0; j--) {
					if (ans[j] != '#') {
						cnt = 0;
					}
					else {
						dis[j] = min(++cnt, dis[j]);
					}
				}

				// 一番遠いい点を探す
				int jmax = -1;
				int dismax = -1;
				for (int j = 0; j < n; j++) {
					if (dismax < dis[j]) {
						jmax = j;
						dismax = dis[j];
					}
				}

				ans[jmax] = a[i];
			}
		}

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

	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<=2&&c==2&&mx<c) {
    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;
}

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++);

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

			if(maxDist < min(ldist,rdist)){
				res = i;
				maxDist = min(ldist,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==0 ? n/2 : n/2 : idx)] = 'C';
				break;
			case 'D':
				s[(i == 0 ? 0 : D())] = 'D';
				break;
			}
		}

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

	return 0;
}