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<stdio.h>
int main(void)
{
    int n,m,i,j,flg,w,d,p,q,k,e[100];
	char s;
	while(1){
		scanf("%d %d",&n,&m);
		if(n==0&&m==0) break;
		for(i=0;i<n;i++) e[i]=0;
		for(i=0;i<m;i++){
			scanf(" %c",&s);
			if(s=='A'){
				for(j=0;j<n;j++){
					if(e[j]==0){
						e[j]=1; 
						break;
					}
				}
			}
			else if(s=='B'){
				flg=0;
				for(j=n-1;j>=0;j--){
					if(e[j]==0){
						if(e[j-1]!=1){
							e[j]=2;
							flg=1; break;
						}
					}
					else if(e[j]==1) j--;
				}
				if(flg==0){
					for(j=0;j<n;j++){
						if(e[j]==0){
							e[j]=2;
							break;
						}
					}
				}
			}
			else if(s=='C'){
				flg=0;
				if(i==0){
					e[n/2]=3;
				}
				else{
					for(j=1;j<n;j++){
						if(e[j-1]!=0&&e[j]==0) e[j]=3;flg=1; break;
					}
					if(flg==0){
						for(j=n-1;j>=0;j--){
							if(e[j]==0) e[j]=3;break;
						}
					}
				}
			}
			else if(s=='D'){
				flg=0;d=0; w=0;q=0;
				if(i==0){
					e[0]=4;
				}
				else {
					for(j=0;j<n;j++){
						if(e[j]==0) d++; flg=1;
						if(flg==1&&e[j]!=0){
							if(w<d){
								w=d;
								p=q;
								k=j-1;
							}
							d=0;
						}
						if(e[j]!=0) q=j;
					}
					e[p+w/2]=4;
				}
			}
		}
		for(i=0;i<n;i++){
			if(e[i]==0) printf("#");
			if(e[i]==1) printf("A");
			if(e[i]==2) printf("B");
			if(e[i]==3) printf("C");
			if(e[i]==4) printf("D");
		}
		printf("\n");
	}
	return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <climits>
using namespace std;

int n, m;
string seat;

void sit(char a) {
    switch (a) {
        case 'A': {
            for (int i=1; i<=n; ++i) {
                if (seat[i] == '#') {
                    seat[i] = 'A'; return ;
                }
            }
            break;
        }
        case 'B': {
            for (int i=n; i>=1; --i) {
                if (seat[i] == '#' && seat[i-1] != 'A' && seat[i+1] != 'A') {
                    seat[i] = 'B'; return ;
                }
            }
            for (int i=1; i<=n; ++i) {
                if (seat[i] == '#') {
                    seat[i] = 'B'; return ;
                }
            }
            break;
        }
        case 'C': {
            bool empty = true;
            for (int i=1; i<=n; ++i) {
                if (seat[i] != '#') {
                    empty = false; break;
                }
            }
            if (empty) {
                seat[(n+2)/2] = 'C'; return ;
            }
            for (int i=1; i<=n; ++i) {
                if (seat[i] != '#') {
                    if (seat[i+1] == '#') {
                        seat[i+1] = 'C'; return ;
                    } else if (seat[i-1] == '#') {
                        seat[i-1] = 'C'; return ;
                    }
                }
            }
            break;
        }
        case 'D': {
            int k, mx = -1;
            for (int i=1; i<=n; ++i) {
                int l = 0;
                while (0 < i-l && seat[i-l] == '#') ++l;
                int r = 0;
                while (i+r < n+1 && seat[i+r] == '#') ++r;

                if (i+r == n+1) r = INT_MAX;
                if (i-l == 0) l = INT_MAX;
                int dist = min(l, r);

                if (mx < dist) {
                    k = i;
                    mx = dist;
                }
            }
            seat[k] = 'D';
            break;
        }
    }
}

int main() {
    while (cin >> n >> m, (n || m)) {
        seat = "_";
        for (int i=0; i<n; ++i) {
            seat += "#";
        }
        seat += "_";
        char a;
        for (int i=0; i<m; ++i) {
            cin >> a;
            sit(a);
        }
        cout << seat.substr(1,n) << endl;
    }
    return 0;
}