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 <cstring>
#include <algorithm>

using namespace std;

int chair[100],pos,n,m;

int d(char c){
	if(c == 'A'){
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}else if(c == 'B'){
		for(int i=n-1;i>=0;i--){
			if(chair[i] == -1){
				if(i == 0){
					if(chair[i+1] != 'A') return i;
				}else if(i == n-1){
					if(chair[i-1] != 'A') return i;
				}else{
					if(chair[i-1] != 'A' && chair[i+1] != 'A') return i;
				}
			}
		}
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}else if(c == 'C'){
		for(int i=0;i<n;i++){
			if(chair[i] != -1){
				if(i+1 < n && chair[i+1] == -1) return i;
				if(0 <= i-1 && chair[i-1] == -1) return i;
			}
		}
		return n/2+1;
	}else{
		int d_min_max = 0,d_pos=-1,tmp;
		for(int i=0;i<n;i++){
			//ó¢Ä¢éÖqÆÅàß¢lÌ£ðßé
			
			if(chair[i] == -1){
				int dist_min = 1 << 28;
				if(i != n-1){
					tmp = 1;
					while(i+tmp < n && chair[i+tmp] == -1) tmp++;
					if(i+tmp<n){
						dist_min = min(dist_min, tmp);
					}
				}
				if(i != 0){
					tmp = 1;
					while(i-tmp >= 0 && chair[i-tmp] == -1) tmp++;
					if(i-tmp >= 0){
						dist_min = min(dist_min, tmp);
					}
				}
				if(d_min_max < dist_min){
					d_min_max = dist_min;
					d_pos = i;
				}
			}
		}
		if(d_pos != -1) return d_pos;
		for(int i=0;i<n;i++){
			if(chair[i] == -1) return i;
		}
	}
}

int main(){
	while(cin >> n >> m){
		if(!(n|m)) break;
		char c;
		memset(chair, -1, sizeof(chair));
		for(int i=0;i<m;i++){
			cin >> c;
			chair[d(c)] = c;
		
		for(int i=0;i<n;i++){
			if(chair[i] == -1){
				cout << "#";
			}else{
				cout << (char)chair[i];
			}
		}
		cout << endl;
	}
	}
}

C++: #include<iostream>
#include<algorithm>
using namespace std;
int main() {
	int n, m;
	while (cin >> m >> n&&n != 0 && m != 0) {
		char a[100];
		fill(a, a + m, '#');
		for (int z = 0; z < n; z++) {
			char b;
			cin >> b;
			switch (b) {
				case 'A':
					for (int i = 0; i < m; i++) {
						if (a[i] == '#') {
							a[i] = 'A';
							break;
						}
					}
					break;
				case 'B': 
					for (int i = m - 1; i >= 0; i--) {
						if ((i == (m - 1) && a[m - 2] != 'A'&&a[i] == '#') || (i == 0 && a[1] != 'A'&&a[i] == '#') || (a[i - 1] != 'A'&&a[i] == '#'&&a[i + 1] != 'A')) {
							a[i] = 'B';
							goto stop;
						}
					}
					for (int i = 0; i < m; i++) {
						if (a[i] == '#') {
							a[i] = 'B';
							break;
						}
					}
				stop:;
					break;
				case 'C':
					if (z == 0) {
						if (m % 2 == 1)
							a[(m + 1) / 2] = 'C';
						else
							a[m / 2 + 1] = 'C';
						goto st;
					}
					for (int i = 1; i < m; i++) {
						if (a[i - 1] != '#'&&a[i] == '#') {
							a[i] = 'C';
							goto st;
						}
					}
				st:;
					break;
				case 'D':
					int f = 0, g = 0;
					if (z == 0) {
						a[0] = 'D'; goto stp;
					}
					for (int i = m - 1; i >= 0; i--) {
						int h = 0, k = 0;
						for (int j = i; j >= 0; j--) {
							if (a[j] != '#')
								break;
							else
								h++;
						}
						for (int j = i; j < m; j++) {
							if (a[j] != '#')
								break;
							else
								k++;
						}
						if (g <= min(h, k)) {
							f = i;
							g = min(h, k);
						}
					}
					a[f] = 'D';
				stp:;
					break;
			}
		}
		for (int i = 0; i < m; i++) {
			cout << a[i];
		}
		cout << endl;
	}
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>

using namespace std;

#define rep(i,j) REP((i), 0, (j))
#define REP(i,j,k) for(int i=(j);(i)<(k);++i)
#define BW(a,x,b) ((a)<=(x)&&(x)<=(b))
#define F first
#define S second
#define INF 1 << 30

typedef pair<int, int> pi;
typedef pair<int, pi> pii;
typedef vector<int> vi;
typedef queue<int> qi;
typedef long long ll;

int n, m, f, dis, pos;
char c[100];

int main(){
  while(scanf("%d%d", &n, &m) && n){
    rep(i, n) c[i] = '#';
    char p[2];
    rep(k, m){
      scanf("%s", p);
      switch(p[0]){
      case 'A':
	rep(i, n) if(c[i] == '#'){ c[i] = 'A'; break;;}
	break;
      case 'B':
	if(c[n-2] != 'A' && c[n-1] == '#'){ c[n-1] = 'B'; break;}
	for(int i = n-2; i > 0; i--) if(c[i+1] != 'A' && c[i-1] != 'A' && c[i] == '#'){ c[i] = 'B'; goto e1;}
	if(c[1] != 'A' && c[0] == '#'){ c[0] = 'B'; break;}
	rep(i, n) if(c[i] == '#'){ c[i] = 'B'; break;}
      e1:
	break;
      case 'C':
	rep(i, n-1) if(c[i] != '#' && c[i+1] == '#'){ c[i+1] = 'C'; goto e2;}
	f = 0;
	rep(i, n) if(c[i] != '#') f = 1;
	if(f){
	  c[0] = 'C';
	}else{
	  if(n%2) c[(n+1)/2] = 'C';
	  else c[n/2+1] = 'C';
	}
      e2:
	break;
      case 'D':
	dis = 0, pos = 0;
	rep(i, n){
	  if(c[i] != '#') continue;
	  int j;
	  f = 0;
	  for(j = 1; j < n; j++){
	    if(i-j >= 0 && c[i-j] != '#') f = 1;
	    //	    printf("%d ", f);
	    if(i+j < n && c[i+j] != '#') f = 1;
	    //	    printf("%d ", f);
	    if(f){
	      if(dis < j){
		dis = j;
		pos = i;
	      }
	      break;
	    }
	  }
	  //	  printf("%d %d %d\n",i, dis, pos);
	}

	c[pos] = 'D';
	break;
      }
    }
  
    rep(i, n) putchar(c[i]); puts("");
  }
  return 0;
}