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;
			break;
		}
	}
	for(int i = k; i >= 1; --i){
		if(chair[i]){
			ret = std::min(ret, k - i);
			break;
		}
	}
	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 <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pll> pip;
const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-9;

int n, m;
int seet[100];

int main() {
	
	while (cin >> n >> m, n || m) {
		memset(seet, -1, sizeof(seet));
		REP(t, m) {
			char c; scanf(" %c", &c);
			
			bool ok = false;
			
			switch (c) {
				case 'A':
					REP(i, n) if (seet[i] == -1) {
						seet[i] = 0;
						break;
					}
				break;
					
				case 'B':
					for (int i = n - 1; i > 0; i--) if (seet[i] == -1) {
						if (seet[i - 1] == 0) i -= 2;
						else {
							seet[i] = 1;
							ok = true;
							break;
						}
					}
					if (ok) break;
					
					REP(i, n) if (seet[i] == -1) {
						seet[i] = 1;
						break;
					}
				break;
					
				case 'C':
					REP(i, n) if (seet[i] != -1) {
						if (i < n - 1 && seet[i + 1] == -1) {
							seet[i + 1] = 2;
							ok = true;
							break;
						}
						if (i > 0 && seet[i - 1] == -1) {
							seet[i - 1] = 2;
							ok = true;
							break;
						}
					}
					if (ok) break;
					seet[n / 2] = 2;
				break;
				
				case 'D':
					pii ma(-1, 0); // ?????¢, ??????
					
					int l = -1, r = 0;
					
					REP(i, n) {
						if (seet[i] == -1) {
							chmax(r, i + 1);
							while (r < n && seet[r] == -1) r++;
							
							int ls = l == -1 ? INF : i - l;
							int rs = r == n ? INF : r - i;
							
							chmax(ma, pii(min(ls, rs), -i));
						}
						else {
							l = i;
						}
					}
					
					if (ma.fi == INF) seet[0] = 3;
					else seet[-ma.se] = 3;
					
				break;
			}
			
		}
		REP(i, n) printf("%c", seet[i] == -1 ? '#' : seet[i] + 'A');
		puts("");
	}
	return 0;
}