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>

int n, m;
int chair[105];

int dist(int k){
	int ret = 1000;
	for(int i = k; i <= n; ++i){
		if(chair[i]){
			ret = i - k;
		}
	}
	for(int i = k; i >= 1; --i){
		if(chair[i]){
			ret = std::min(ret, k - i);
		}
	}
	return ret;
}

int main(){
	while(true){
		for(int i = 0; i < 105; ++i)chair[i] = 0;
		
		std::cin >> n >> m;
		if(n == 0 && m == 0)break;

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

			if(ch == 'A'){
				for(int j = 1; j <= n; ++j){
					if(chair[j] == 0){
						chair[j] = 1;
						break;
					}
				}
			}
			else if(ch == 'B'){
				bool f = false;

				for(int j = n; j >= 1; --j){
					if(chair[j] == 0 && chair[j - 1] != 1 && chair[j + 1] != 1){
						chair[j] = 2;
						f = true;
						break;
					}
				}

				if(!f){
					for(int j = 1; j <= n; ++j){
						if(chair[j] == 0){
							chair[j] = 2;
							break;
						}
					}
				}
			}
			else if(ch == 'C'){
				if(i == 0)chair[n % 2 ? ((n + 1) / 2) : (n / 2 + 1)] = 3;
				else{
					for(int j = 1; j <= n; ++j){
						if(chair[j]){
							if(j + 1 <= n && chair[j + 1] == 0){
								chair[j + 1] = 3;
								break;
							}
							if(j - 1 >= 1 && chair[j - 1] == 0){
								chair[j - 1] = 3;
								break;
							}
						}
					}
				}
			}
			else if(ch == 'D'){
				if(i == 0)chair[1] = 4;
				else{
					int maxV = -1000, maxI;
					for(int j = 1; j <= n; ++j){
						if(chair[j] == 0){
							if(dist(j) > maxV)maxV = dist(j), maxI = j;
						}
					}
					chair[maxI] = 4;
				}
			}
		}

		for(int i = 1; i <= n; ++i){
			if(chair[i] == 0)std::cout << "#";
			else std::cout << (char)('A' + chair[i] - 1);
		}
		std::cout << std::endl;
	}
	
	return 0;
}

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(t == n-1)
					tmp1 = n+1;
			}
		}
		else
			tmp1 = n+1;
		if(k>0){
			for(int t=k-1; t>=0; t--){
				if(chr[t] != '#')
					break;
				tmp2++;
				if(t == 0)
					tmp2 = n+1;
			}
		}
		else
			tmp2 = n+1;
		if(tmp1 > tmp2)
			tmp1 = tmp2;
		if(tmp1 > tmp){
			tmp = tmp1;
			ans = k;
		}
		std::cout << tmp1 << ' ';
	}
	std::cout << '\n';
	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;
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

#define MAX 10000
char C[MAX + 2];
int n, m;
void setLeft(char ch) {
	for (int i = 1;; i++) {
		if (C[i] == '#') {
			C[i] = ch;
			return;
		}
	}
}
void setB() {
	for (int i = n; i >= 1; i--) {
		if (C[i] == '#' && C[i - 1] != 'A' && C[i + 1] != 'A') {
			C[i] = 'B';
			return;
		}
	}
	setLeft('B');
}
bool isEmpty() {
	for (int i = 1; i <= n; i++)
		if (C[i] != '#')
			return false;
	return true;
}
void setC() {
	if (isEmpty()) {
		C[n / 2 + 1] = 'C';
		return;
	}
	for (int i = 1; i <= n; i++) {
		if (C[i] == '#')
			continue;
		if (C[i + 1] == '#') {
			C[i + 1] = 'C';
			return;
		}
		if (C[i - 1] == '#') {
			C[i - 1] = 'C';
			return;
		}
	}
}
int getDist(int p) {
	int l = 0, r = 0;
	while (C[p + l - 1] == '#')
		l--;
	if (C[p + l - 1] == 'X')
		l = -1000000;
	while (C[p + r + 1] == '#')
		r++;
	if (C[p + r + 1] == 'X')
		r = 1000000;
	return min((-1) * l, r);
}
void setD() {
	if (isEmpty()) {
		C[1] = 'D';
		return;
	}
	int d, mi, md = -1;
	for (int i = 1; i <= n; i++) {
		if (C[i] != '#')
			continue;
		d = getDist(i);
		if (d > md) {
			md = d;
			mi = i;
		}
	}
	C[mi] = 'D';
}
main() {
	char ch;
	while( cin >> n >> m && n && m ) {
		for(int i = 0;i<=n+1;i++) C[i] = '#';
		C[0] = C[n+1] = 'X';
		for(int i = 1;i<=m;i++) {
			cin >> ch;
			if ( ch == 'A' ) setLeft('A');
			else if ( ch == 'B' ) setB();
			else if ( ch == 'C' ) setC();
			else if ( ch == 'D' ) setD();
		}
		for(int i = 1;i<=n;i++) cout << C[i];
		cout << endl;
	}
}