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 <cstring>
#include <algorithm>

using namespace std;

int chair[100],pos,n,m;

int d(char c){
	if(c == 'A'){
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}else if(c == 'B'){
		for(int i=n-1;i>=0;i--){
			if(chair[i] == -1){
				if(i == 0){
					if(chair[i+1] != 'A') return i;
				}else if(i == n-1){
					if(chair[i-1] != 'A') return i;
				}else{
					if(chair[i-1] != 'A' && chair[i+1] != 'A') return i;
				}
			}
		}
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}else if(c == 'C'){
		for(int i=0;i<n;i++){
			if(chair[i] != -1){
				if(i+1 < n && chair[i+1] == -1) return i+1;
				if(0 <= i-1 && chair[i-1] == -1) return i-1;
			}
		}
		return n/2+1;
	}else{
		int d_min_max = 0,d_pos=-1,tmp;
		for(int i=0;i<n;i++){
			//ó¢Ä¢éÖqÆÅàß¢lÌ£ðßé
			
			if(chair[i] == -1){
				int dist_min = 1 << 28;
				if(i != n-1){
					tmp = 1;
					while(i+tmp < n && chair[i+tmp] == -1) tmp++;
					if(i+tmp<n){
						dist_min = min(dist_min, tmp);
					}
				}
				if(i != 0){
					tmp = 1;
					while(i-tmp >= 0 && chair[i-tmp] == -1) tmp++;
					if(i-tmp >= 0){
						dist_min = min(dist_min, tmp);
					}
				}
				if(d_min_max < dist_min && dist_min != 1 << 28){
					d_min_max = dist_min;
					d_pos = i;
				}
			}
		}
		if(d_pos != -1) return d_pos;
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}
}

int main(){
	while(cin >> n >> m){
		if(!(n|m)) break;
		char c;
		memset(chair, -1, sizeof(chair));
		for(int i=0;i<m;i++){
			cin >> c;
			chair[d(c)] = c;
		}
		for(int i=0;i<n;i++){
			if(chair[i] == -1){
				cout << "#";
			}else{
				cout << (char)chair[i];
			}
		}
		cout << endl;
	}
}

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

char ch[1000];
int n,m;

int putA(char x){
	for(int i = 1 ; i <= n ; i++){
		if( ch[i] == '#' ){
			ch[i] = x;
			break;
		}
	}
	return 0;
}
int putB(char x){
	for(int i = n ; i >= 1 ; i--){
		if(ch[i-1] != 'A' && ch[i+1] != 'A' ){
			ch[i] = x;
			return 0;
		}
	}
	// else
	putA(x);
}

int putC(char x){
	
	for(int i = 1 ; i <= n ; i++){
		if( ch[i] != '#'){
			if( i+1 <= n && ch[i+1] == '#' ){ ch[i+1] = x; return 0; }
			if( i-1 >= 1 && ch[i-1] == '#' ){ ch[i-1] = x; return 0; }
		}
	}
	if( n % 2 ){
		ch[(n+1)/2] = x;
	}else{
		ch[n/2+1] = x;
	}
}
int putD(char x){
	int distance = 0 , idx = 0;
	for(int i = 1 ; i <= n ; i++){
		int best = 10000;
		for(int j = 1 ; j <= n ; j++){
			if( ch[j] != '#' ) best = min(abs(i-j),best);
		}
		if( best > distance ){
			idx = i;
			distance = best;
		}
	}
	ch[idx] = x;
}
int main(){
	while(cin >> n >> m && n){
		for(int i = 0 ; i < 1000 ; i++) ch[i] = '#';
		for(int i = 0 ; i < m ; i++){
			char c;
			cin >> c;
			if( c == 'A' ) putA(c);
			if( c == 'B' ) putB(c);
			if( c == 'C' ) putC(c);
			if( c == 'D' ) putD(c);

		}
			for(int i = 1 ; i <= n ; i++)
				cout << ch[i];
			cout << endl;


	}
}