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 <algorithm>

using namespace std;

int main()
{
	for(int n,m;cin>>n>>m,n|m;){
		string s(n,'#');
		while(m--){
			char p; cin>>p;
			if(p=='A'){
				for(int i=0;i<n;i++)
					if(s[i]=='#'){
						s[i]='A';
						break;
					}
			}
			if(p=='B'){
				bool flg=false;
				for(int i=n-1;i>=0;i--){
					if(s[i]=='#' && (i==n-1 || s[i+1]!='A') && (i==0 || s[i-1]!='A')){
						s[i]='B';
						flg=true;
						break;
					}
				}
				if(!flg){
					for(int i=0;i<n;i++)
						if(s[i]=='#'){
							s[i]='A';
							break;
						}
				}
			}
			if(p=='C'){
				if(count(s.begin(),s.end(),'#')==n)
					s[s.size()/2]='C';
				else{
					for(int i=0;i<n;i++){
						if(s[i]=='#')
							continue;
						if(i<n-1 && s[i+1]=='#'){
							s[i+1]='C';
							break;
						}
						if(i>0 && s[i-1]=='#'){
							s[i-1]='C';
							break;
						}
					}
				}
			}
			if(p=='D'){
				if(count(s.begin(),s.end(),'#')==n)
					s[0]='D';
				else{
					int mi=-1,md;
					for(int i=0;i<n;i++){
						if(s[i]!='#')
							continue;
						int d=n;
						for(int j=i-1;j>=0;j--)
							if(s[j]!='#'){
								d=min(d,i-j);
								break;
							}
						for(int j=i+1;j<n;j++)
							if(s[j]!='#'){
								d=min(d,j-i);
								break;
							}
						if(mi==-1 || d<md){
							mi=i;
							md=d;
						}
					}
					s[mi]='D';
				}
			}
		}
		cout<<s<<endl;
	}
	
	return 0;
}

C++: #include<iostream>
#include<string.h>
#include<cstdio>
using namespace std;
int main() {
	int n, m, temp;
	char str, str2[101], str3[101] = { NULL };
	while (1) {
		cin >> n >> m;
		if (n == 0 && m == 0)return 0;
		for (int i = 0; i < m; i++) {
			cin >> str2[i];
		}
		for (int i = 0; i < n; i++) {
			str3[i] = '#';
		}
		for (int i = 0; i < m; i++) {
			if (str2[i] == 'A') {
				for (int j = 0; j < n; j++) {
					if (str3[j] == '#') {
						str3[j] = 'A';
						goto end;
					}
				}
			}
			else if (str2[i] == 'B') {
				for (int j = n - 1; j > 0; j--) {
					if (str3[j] == '#'&&str3[j - 1] != 'A'&&str3[j + 1] != 'A') {
						str3[j] = 'B';
						temp++;
						goto end;
					}
				}
				if (temp == 0) {
					for (int j = 0; j < n; j++) {
						if (str3[j] == '#') {
							str3[j] = 'B';
							temp++;
							goto end;
						}
					}
				}
				if (temp == 0) {
					for (int j = 0; j < n; j++) {
						if (str3[j] == '#') {
							str3[j] = 'B';
							goto end;
						}
					}
				}
				temp = 0;
			}
			else if (str2[i] == 'C') {
				for (int j = 0; j < n; j++) {
					if (str3[j] != '#') {
						if (str3[j + 1] == '#') {
							str3[j + 1] = 'C';
							temp++;
							goto end;
						}
					}
				}
				if (temp == 0) {
					if (n % 2 == 0)temp = n / 2 + 1;
					else temp = (n + 1) / 2;
					for (int j = 0; j < n; j++) {
						//if (str3[j] == '#')/*goto end*/;
						if (j == n - 1)str3[temp] = 'C';
					}
				}
				temp = 0;
			}
			else if (str2[i] == 'D') {
				temp = 0;
				int gun = 0, x, y;
				for (int j = 0; j < n; j++) {
					int  q = 0, w = 0;
					if (str3[j] == '#') {
						x = y = j;
						while (1) {
							x++;
							y--;
							if (x <= n || y > 0) {
								if (str3[x] == '#' &&x <= n) {
									q++;
									if (gun < q && gun>0) {
										str3[x] = 'D';
										str3[gun] = '#';
										gun = q;
										temp++;
									}
								}
								if (str3[y] == '#' &&y > 0) {
									w++;
									if (gun < w&& gun>0) {
										str3[y] = 'D';
										str3[gun] = '#';
										gun = w;
										temp++;
									}
								}
							}
							else {
								goto loop;
							}
						}
					}
				}
			loop:
				if (temp == 0) {
					for (int j = 0; j < n; j++) {
						if (str3[j] == '#') {
							str3[j] = 'D';
							goto end;
						}
						if (j == n - 1) {
							str3[0] = 'D';
						}
					}
				}
				temp = 0;
			}
		end:;
			/*for (int i = 0; i < n; i++) {
				cout << str3[i];
			}
			cout << endl;*/
		}
		for (int i = 0; i < n; i++) {
			cout << str3[i];
		}
		cout << endl;
		memset(str3, 0, sizeof(str3));
		memset(str2, 0, sizeof(str2));
		temp = 0;
	}
}