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 <bits/stdc++.h>
using namespace std;
// 12:46

string chair;


int goA(char c){
	for(int i = 0 ; i < chair.size() ; i++)
		if( chair[i] == '#'){
			chair[i] = c;
			return 1;
		}
	return 0;
}
int goB(char c){
	for(int i = chair.size() -1  ; i >= 0 ; i--)
		if( chair[i] == '#' && (!i||chair[i-1]!='A') && (i+1==chair.size()||chair[i+1]!='A') ){
			chair[i] = c;
			return 1;
		}
	return goA(c);
}
int goC(char c){
	if( count(chair.begin(),chair.end(),'#') == chair.size() ){
		if( chair.size() % 2 ) chair[(1+chair.size())/2-1] = c;
		else chair[chair.size()/2] = c;
		return 1;
	}
	for(int i = 0 ; i < chair.size() ; i++)
		if( chair[i] != '#'){
			for(int j = 1 ; j >= -1 ; j--){
				if( i+j >= 0 && i+j < chair.size() && chair[i+j] == '#' ){
					chair[i+j] = c;
					return 1;
				}
			}
		}

	return 0;
}
int goD(char c){
	int pos;
	int dst = 2e9;
	for(int i = 0 ; i < chair.size() ; i++){
		if( chair[i] == '#' ){
			int dist = 1e9;
			for(int j = 0 ; j < chair.size() ; j++)
				if( chair[j] != '#') dist = min(dist,abs(i-j));

			if( dst > dist){
				dst = dist;
				pos = i;
			}
		}
	}
	chair[pos] = c;
	return 1;
}


int main(){
	int n,m;
	while( cin >> n >> m && n ){
		chair = string(n,'#');
		for(int i = 0 ; i < m ; i++){
			char c; cin >> c;
			if( c == 'A' ) goA(c);
			if( c == 'B' ) goB(c);
			if( c == 'C' ) goC(c);
			if( c == 'D' ) goD(c);
		}
		cout << chair << endl;
	}
}

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

int main() {
	int n, m;
	const char output[] = { '#', 'A', 'B', 'C', 'D' };
	std::vector<int> seat;
	
	while (std::cin >> n >> m) {
		if (n == 0 && m == 0)
			break;

		seat.resize(n);

		for (int i = 0; i < m; ++i) {
			char who;
			std::cin >> who;

			if (who == 'A') {
				for (int j = 0; j < n; ++j) {
					if (seat[j] == 0) {
						seat[j] = 1;
						break;
					}
				}
			}
			else if (who == 'B') {
				int firstEmpty = 334;
				bool isRightA = false;

				for (int j = n - 1; j >= 0; --j) {
					if (seat[j] == 0) {
						firstEmpty = std::min(firstEmpty, j);
						if (!isRightA && (j == 0 || seat[j - 1] != 1)) {
							seat[j] = 2;
							break;
						}
					}
					isRightA = seat[j] == 1;
				}
			}
			else if (who == 'C') {
				for (int j = 0; j < n; ++j) {
					if (j != 0) {
						if (j != n - 1 && seat[j + 1] == 0) {
							seat[j + 1] = 2;
							break;
						}
						if (j != 0 && seat[j - 1] == 0) {
							seat[j - 1] = 2;
							break;
						}
					}
					if (j == n - 1)
						seat[n / 2] = 2;
				}
			}
			else if (who == 'D') {
				int maxDist = 334;
				int maxIdx = 0;

				int dist = 0;

				int fromTop = 0;
				int toLast = 0;

				for (int j = 0; j < n; ++j) {
					++dist;
					if (j == n - 1)
						toLast = dist;

					if (seat[j] != 0) {
						if (fromTop == 0)
							fromTop = j + 1;

						if (maxDist < dist / 2) {
							maxDist = dist / 2;
							maxIdx = j - dist;
						}
						dist = 0;
					}
				}

				if (seat[n - 1] == 0 && toLast > maxDist && fromTop < toLast)
					seat[n - 1] = 3;
				else if (seat[0] == 0 && fromTop > maxDist && fromTop > toLast)
					seat[0] = 3;
				else
					seat[maxIdx + maxDist] = 3;
			}
		}

		for (int i = 0; i < m; ++i)
			std::cout << output[i];
		std::cout << std::endl;
		seat.clear();
	}

	return 0;
}

C++: #include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<cstdio>
#include<sstream>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mp make_pair
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
const double EPS=1e-10;
const int inf=1e8;
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
int main(){
	int n,m;
	while(cin>>n>>m,n){
		vector<string>in(n,"");
		rep(q,m){
			string s;cin>>s;
			if(s=="A"){
				rep(i,n)if(in[i]==""){
					in[i]="A";
					break;
				}
			}else if(s=="B"){
				vector<string>tmp=in;
				rep(i,n)if(in[i]=="A"){
					if(i)tmp[i-1]="!";
					if(i!=n-1)tmp[i+1]="!";
				}
				int I=inf;
				for(int i=n-1;i>=0;i--)if(tmp[i]==""){I=i;break;}
				if(I==inf){
					rep(i,n)if(in[i]==""){
						I=i;
						break;
					}
				}
				in[I]="B";
			}else if(s=="C"){
				int I=inf;
				rep(i,n)if(in[i]==""){
					if((i&&in[i-1]!="")||(i!=n-1&&in[i+1]!="")){
						I=i;
						break;
					}
				}
				if(I==inf)I=n/2;
				in[I]="C";
			}else{
				if(!q){
					in[0]="D";
					continue;
				}
				vi t;
				rep(i,n)if(in[i]!="")t.pb(i);
				int mi=inf,mii=0;
				if(t[0]!=0){mi=t[0];mii=0;}
				rep(i,t.size()-1)if(t[i+1]-t[i]>1){
					if(mi>(t[i+1]-t[i])/2){
						mi=(t[i+1]-t[i])/2;
						mii=t[i]+(t[i+1]-t[i])/2;
					}
				}
				if(t[t.size()-1]!=n-1&&mi>n-t[t.size()-1]-1){
					mii=n-1;
				}
				in[mii]="D";
			}
		}
		rep(i,n)cout<<(in[i]==""?"#":in[i]);
		cout<<endl;
	}
}