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<string.h>
#include<cstdio>
using namespace std;
int main() {
	int n, m, temp;
	char str, str2[10001], str3[10001] = { 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';
							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;
						}
					}
				}
				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;
	}
}

C++: #include<iostream>

char *chr, *peo;
int n,m;

void sitA(int i){
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'A';
				break;
		}
	}
	return;
}

void sitB(int i){
	if(chr[n-1]=='#' && chr[n-2] != 'A'){
		chr[n-1] = 'B';
		return;
	}
	for(int k=n-2; k>0; k--){
		if(chr[k] == '#' && chr[k-1] != 'A' && chr[k+1] != 'A'){
			chr[k] = 'B';
			return;
		}
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'B';
			return;
		}
	}
}

void sitC(int i){
	if(i==0){
		if(n%2 == 0)
			chr[n/2] = 'C';
		else
			chr[(n-1)/2] = 'C';
		return;
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#')
			continue;
		if(k<n-1){
			if(chr[k+1] == '#'){
				chr[k+1] = 'C';
				return;
			}
		}
		if(k>0){
			if(chr[k-1] == '#'){
				chr[k-1] = 'C';
				return;
			}
		}
	}
}

void sitD(int i){
	if(i==0){
		chr[0] = 'D';
		return;
	}
	int ans,tmp=0,tmp1,tmp2;
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			ans = k;
			break;
		}
	}
	for(int k=ans; k<n; k++){
		if(chr[k] != '#')
			continue;
		tmp1=0;
		tmp2=0;
		if(k<n-1){
			for(int t=k+1; t<n; t++){
				if(chr[t] != '#')
					break;
				tmp1++;
			}
		}
		if(k>0){
			for(int t=k-1; t>=0; t--){
				if(chr[t] != '#')
					break;
				tmp2++;
			}
		}
		if(tmp1 > tmp2)
			tmp1 = tmp2;
		if(tmp1 > tmp){
			tmp = tmp1;
			ans = k;
		}
	}
	chr[ans] = 'D';
}

void solve(){
	char tmp;
	for(int i=0; i<m; i++){
		tmp = peo[i];
		switch(tmp){
		case 'a':
		case 'A':
			sitA(i);
			break;
		case 'b':
		case 'B':
			sitB(i);
			break;
		case 'c':
		case 'C':
			sitC(i);
			break;
		case 'd':
		case 'D':
			sitD(i);
			break;
		}
	}
	std::cout << chr << std::endl;
}

int main(){
	while(true){
		std::cin >> n >> m;
		if(!n && !m)
			return 0;
		chr = new char[n];
		peo = new char[m];
		for(int i=0; i<n; i++){
			chr[i] = '#';
			if(i>=m)
				chr[i] = '#';
			else
				std::cin >> peo[i];
		}
		solve();
		delete[] chr;
		delete[] peo;
	}
}