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 <stdio.h>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>

using namespace std;

struct Info{
	Info(){
		country = '#';
	}
	char country;
};

void func(int n,int m){
	Info info[n];
	char tmp[2];
	int maximum,most_left_index,pre_index,div,left_dist;
	bool FLG;

	for(int loop = 0; loop < m; loop++){
		scanf("%s",tmp);

		switch(tmp[0]){
		case 'A':
			for(int i = 0; i < n; i++){
				if(info[i].country == '#'){
					info[i].country = 'A';
					break;
				}
			}
			break;
		case 'B':
			FLG = false;

			if(info[n-1].country == '#' && info[n-2].country != 'A'){
				info[n-1].country = 'B';
				break;
			}

			for(int i = n-2; i >= 1; i--){
				if(info[i].country == '#' && info[i-1].country != 'A' && info[i+1].country != 'A'){
					info[i].country = 'B';
					FLG = true;
					break;
				}
			}

			if(FLG)break;

			if(info[0].country == '#' && info[1].country != 'A'){
				info[0].country = 'B';
				break;
			}

			for(int i = 0; i < n; i++){
				if(info[i].country == '#'){
					info[i].country = 'B';
					break;
				}
			}
			break;
		case 'C':
			if(loop == 0){
				if(n%2 == 1){
					info[(n+1)/2].country = 'C';
				}else{
					info[(n/2)+1].country = 'C';
				}
			}else{
				FLG = false;
				if(info[0].country != '#' && info[1].country == '#'){
					info[1].country = 'C';
					break;
				}
				for(int i = 1; i <= n-2; i++){
					if(info[i].country != '#'){
						if(info[i+1].country == '#'){
							info[i+1].country = 'C';
							FLG = true;
							break;
						}else if(info[i-1].country == '#'){
							info[i-1].country = 'C';
							FLG = true;
							break;
						}
					}
					if(FLG)break;
				}
				if(FLG)break;

				if(info[n-1].country != '#' && info[n-2].country == '#'){
					info[n-2].country = 'C';
					break;
				}
			}
			break;
		case 'D':

			if(loop == 0){
				info[0].country = 'D';
			}else{
				maximum = 0;
				most_left_index = -1;
				pre_index = -1;

				if(info[0].country == '#'){
					most_left_index = 0;
					for(div = 1; div <= n-1; div++){
						if(info[div].country != '#'){
							break;
						}
					}
					maximum = div;
				}else{
					pre_index = 0;
				}

				for(int i = 1; i <= n-1; i++){
					if(info[i].country == '#'){

						left_dist = i - pre_index;

						if(i <= n-2){
							for(div = 1; i+div <= n-1; div++){
								if(info[i+div].country != '#'){
									break;
								}
							}
						}else{ //i == n-1
							div = left_dist;
						}

						div = min(left_dist,div);

						if(div > maximum){
							maximum = div;
							most_left_index = i;
						}
					}else{
						pre_index = i;
					}
				}

				info[most_left_index].country = 'D';
			}

			break;
		}
	}

	for(int i = 0; i < n; i++)printf("%c",info[i].country);
	printf("\n");
}

int main(){

	int n,m;
	while(true){
		scanf("%d %d",&n,&m);
		if(n == 0 && m == 0)break;

		func(n,m);

	}

    return 0;
}

C++: 
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>
#include<limits>

#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ll, char> plc;

int main()
{
	int m, n;
	while (cin >> n >> m, n, m) 
	{
		int a[110] = { 0 };
		for (int i = 0; i < m; i++) 
		{
			char c; cin >> c;
			if (c == 'A') 
			{
				for (int j = 0; j < n; j++)if (!a[j]) { a[j] = 1; break; }
			}
			if (c == 'B') 
			{
				for (int j = n - 1; j >= 0; j--)if (!a[j]) { a[j] = 2; break; }
			}
			if(c == 'C')
			{
				if (!i)a[n / 2] = 3;
				else
				{
					for (int j = 0; j < n; j++) 
					{
						if (j != n - 1 && a[j] && !a[j + 1]) { a[j + 1] = 3; break; }
						if (j && a[j] && !a[j - 1]) { a[j - 1] = 3; break; }
					}
				}
			}
			if (c == 'D') 
			{
				if (!i)a[0] = 4;
				else
				{
					int mc = -1, mi = -1, x, y;
					for (int j = 0; j < n; j++) 
					{
						x = y = 999;
						for (int k = j; k >= 0; k--)if (a[k]) { x = j - k; break; }
						for (int k = j; k < n; k++)if (a[k]) { y = k - j; break; }
						if (x > y)x = y;
						if (mc < x)mc = x, mi = j;
					}
					a[mi] = 4;
				}
			}
		}
		for (int j = 0; j < n; j++)putchar("#ABCD"[a[j]]);
		puts("");
	}
	return 0;
}