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 <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <sstream>
#include <climits>
#include <cfloat>
#include <complex>

using namespace std;

int main()
{
	int n, m;
	while (scanf("%d %d", &n, &m), n | m)
	{
		char t[102];	// 1~n
		memset(t, '#', sizeof(t));
		for (int w = 0; w < m; ++w)
		{
			char c;
			scanf(" %c", &c);
			if (c == 'A')
			{
				int i;
				for (i = 1; t[i] != '#'; ++i)
					;
				t[i] = 'A';
			}
			else if (c == 'B')
			{
				int i;
				for (i = n; i >= 1; --i)
					if (t[i-1] != 'A' && t[i] == '#' && t[i+1] != 'A')
						break;
				if (i == 0)
					for (i = 1; t[i] != '#'; ++i)
						;
				t[i] = 'B';
			}
			else if (c == 'C')
			{
				int i;
				if (w == 0)
					i = n / 2 + 1;
				else
				{
					for (i = 2; ; ++i)
						if (t[i-1] != '#' && t[i] == '#')
							break;
					if (i == n+1)
						for (--i; t[i] != '#'; --i)
							;
				}
				t[i] = 'C';
			}
			else
			{
				int i;
				if (w == 0)
					i = 1;
				else
				{
					int dis[102];
					for (int j = 0; j < 102; ++j)
						dis[j] = 100000000;
					for (int j = 1; j <= n; ++j)
					{
						if (t[j] != '#')
							for (int k = 1; k <= n; ++k)
								dis[k] = min(dis[k], abs(j-k));
					}
					int d = 0;
					for (int j = 1; j <= n; ++j)
					{
						if (dis[j] > d)
						{
							i = j;
							d = dis[j];
						}
					}
				}
				t[i] = 'D';
			}
			printf("%2d: ", w);
					for (int i = 1; i <= n; ++i)
			putchar(t[i]);
					printf("\n");
		}
		for (int i = 1; i <= n; ++i)
			putchar(t[i]);
		printf("\n");
	}

	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] != '#')
			continue;
		tmp1=0;
		tmp2=0;
		for(int t=k; t<n; t++){
			if(chr[t] != '#')
				break;
			tmp1++;
			if(t == n-1)
				tmp1 = n+1;
		}
		if(k == n-1)
			tmp1 = n+1;
		for(int t=k; t>=0; t--){
			if(chr[t] != '#')
				break;
			tmp2++;
			if(t == 0)
				tmp2 = n+1;
		}
		if(k == 0)
			tmp2 = n+1;
		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)
				std::cin >> peo[i];
		}
		solve();
		delete[] chr;
		delete[] peo;
	}
}

C++: #include<iostream>
#include<algorithm>
#include<cstdio>
using namespace std;
#define INF (1 << 29)
int main(){
  char chair[105];
  int n, m;
  char c;
  while(cin >> n >> m, n){
    fill(chair, chair + n, '#');
    chair[n] = 0;
    for(int i = 0;i < m;i++){
      cin >> c;
      switch(c){
      case 'A':
      left :
	for(int j = 0;j < n;j++){
	  if(chair[j] == '#'){
	    chair[j] = c;
	    break;
	  }
	}
	break;
      case 'B':
	for(int j = n - 1;j >= 0;j--){
	  if((j == 0 || chair[j - 1] != 'A') && chair[j + 1] != 'A' && chair[j] == '#'){
	    chair[j] = c;
	    break;
	  }
	  if(j == 0)goto left;
	}
	break;
      case 'C':
	for(int j = 0;j < n;j++){
	  if(chair[j] != '#'){
	    if(chair[j + 1] == '#'){
	      chair[j + 1] = c;
	      break;
	    }
	    if(j != 0 && chair[j - 1] == '#'){
	      chair[j - 1] = c;
	      break;
	    }
	  }
	  if(j == n - 1){
	    chair[n / 2] = c;
	  }
	}
	break;
      case 'D':
	int p = 0, s = -1;
	for(int j = 0;j < n;j++){
	  if(chair[j] != '#')continue;
	  int t = INF;
	  for(int k = j;k < n;k++){
	    if(chair[k] != '#'){
	      t = k - j;
	      break;
	    }
	  }
	  for(int k = j;k >= 0;k--){
	    if(chair[k] != '#'){
	      t = min(t, j - k);
	      break;
	    }
	  }
	  if(t > s){
	    p = j;
	    s = t;
	  }
	}
	if(p == INF){
	  chair[n - 1] = c;
	}
	else{
	  chair[p] = c;
	}
	break;
      }
    }
    printf("%s\n", chair);
  }
  return 0;
}