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>
using namespace std;
#define rep(i,s,e) for ( int i = s; i <= e; i++ )
#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(){
    rep(i,1,n) if ( C[i] != '#' ) return false;
    return true;
}

void setC(){
    if ( isEmpty() ){ C[n/2+1] = 'C'; return; }
    rep(i,1,n){
	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;
    rep(i,1,n){
	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 ){
      assert( n <= 100 );
	rep(i,0,n+1) C[i] = '#';
	C[0] = C[n+1] = 'X';
	rep(i,1,m){ 
	    cin >> ch;
	    if ( ch == 'A' ) setLeft('A');
	    else if ( ch == 'B' ) setB();
	    else if ( ch == 'C' ) setC();
	    else if ( ch == 'D' ) setD();
	}
	rep(i,1,n) cout << C[i];
	cout << endl;
    }
}

C++: #include<iostream>
#include<algorithm>
using namespace std;
int x[1001], n, m; char c;
void _a() {
	for (int i = 1; i <= n; i++) {
		if (x[i] == 0) { x[i] = 1; return; }
	}
}
void _b() {
	for (int i = n; i >= 1; i--) {
		if (x[i] == 0 && x[i - 1] != 1 && x[i + 1] != 1) {
			x[i] = 2; return;
		}
	}
	for (int i = 1; i <= n; i++) {
		if (x[i] == 0) { x[i] = 2; return; }
	}
}
void _c() {
	for (int i = 1; i <= n; i++) {
		if (x[i] >= 1) {
			if (x[i + 1] == 0 && i < n) { x[i + 1] = 3; return; }
			if (x[i - 1] == 0 && i >= 2) { x[i - 1] = 3; return; }
		}
	}
	if (n % 2 == 0) { x[(n / 2) + 1] = 3; }
	else { x[(n + 1) / 2] = 3; }
}
void _d(int p) {
	int dist[1000];
	for (int i = 0; i < 1000; i++) { dist[i] = 10000000; }
	if (p == 0) { x[1] = 4; return; }
	for (int i = 1; i <= n; i++) {
		if (x[i] == 0) { continue; }
		for (int j = 1; j <= n; j++) {
			int D = i - j;
			if (D < 0) { D = -D; }
			dist[j] = min(dist[j], D);
		}
	}
	int maxn = 0, maxid = 0;
	for (int i = 1; i <= n; i++) {
		if (maxn < dist[i]) { maxn = dist[i]; maxid = i; }
	}
	x[maxid] = 4;
}
int main() {
	while (true) {
		cin >> n >> m; if (n == 0 && m == 0) { break; }
		for (int i = 1; i <= 1000; i++) { x[i] = 0; }
		for (int i = 0; i < m; i++) {
			cin >> c;
			int d = c - 'A' + 1;
			if (d == 1) { _a(); }
			if (d == 2) { _b(); }
			if (d == 3) { _c(); }
			if (d == 4) { _d(i); }
		}
		for (int i = 1; i <= n; i++) {
			if (x[i] == 0) { cout << '#'; }
			if (x[i] == 1) { cout << 'A'; }
			if (x[i] == 2) { cout << 'B'; }
			if (x[i] == 3) { cout << 'C'; }
			if (x[i] == 4) { cout << 'D'; }
		}
		cout << endl;
	}
	return 0;
}

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] == '#' && chair[j + 1] != 'A'){
	    chair[j] = c;
	    break;
	  }
	  if(j == 0)goto left;
	}
	break;
      case 'C':
	for(int j = 0;j < n;j++){
	  if(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;
	    }
	  }
	  for(int k = j;k >= 0;k--){
	    if(chair[k] != '#'){
	      t = min(t, j - k);
	    }
	  }
	  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;
}