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>
using namespace std;
int main(){
  int n,m;
  while(cin >>n>>m,n||m){
    int row[100] = {0},chair[102] = {0};
    for(int i=0; i<m; i++){
      string s;
      cin >>s;
      if(s == "A"){row[i] = 1;}
      if(s == "B"){row[i] = 2;}
      if(s == "C"){row[i] = 3;}
      if(s == "D"){row[i] = 4;}
    }
    for(int i=0; i<m; i++){
      if(row[i] == 1){
	for(int j=0; j<n; j++){
	  if(!chair[j+1]){
	    chair[j+1] = 1;
	    break;
	  }
	}
      }
      if(row[i] == 2){
	bool non = true;
	for(int j=n-1; j>=0; j--){
	  if(chair[j] != 1 && chair[j+1] == 0 && chair[j+2] != 1){
	    chair[j+1] = 2;
	    non = false;
	    break;
	  }
	}
	if(non){
	  for(int j=0; j<n; j++){
	    if(!chair[j+1]){
	      chair[j+1] = 2;
	      break;
	    }
	  }
	}
      }
      if(row[i] == 3){
	if(!i){
	  if(n%2){chair[(n+1)/2] = 3;}
	  else{chair[n/2+1] = 3;}
	}
	else{
	  for(int j=1; j<=n; j++){
	    if(chair[j] && !chair[j+1] && j < n-1){
	      chair[j+1] = 3;
	      break;
	    }
	    if(chair[j] && !chair[j-1] && j){
	      chair[j-1] = 3;
	      break;
	    }
	  }
	}
      }
      if(row[i] == 4){
	if(!i){chair[1] = 4;}
	else{
	  int r = 0,s = -1;
	  bool non = true;
	  for(int j=0; j<n; j++){
	    if(!chair[j+1]){
	      int x = 200;
	      for(int k=j+1; k<n; k++){
		if(chair[k+1]){
		  if(x > k-j){x = k-j;}
		  break;
		}
	      }
	      for(int k=j-1; k>=0; k--){
		if(chair[k+1]){
		  if(x > j-k){x = j-k;}
		  break;
		}
	      }
	      if(r < x){r = x;s = j;}
	    }
	  }
	  if(s != -1){
	    chair[s+1] = 4;
	    non = false;
	  }
	  if(non){
	    for(int j=0; j<n; j++){
	      if(!chair[j+1]){
		chair[j+1] = 4;
		break;
	      }
	    }
	  }
	}
      }
    }
    for(int i=0; i<n; i++){
      if(chair[i+1] == 0){cout <<"#";}
      if(chair[i+1] == 1){cout <<"A";}
      if(chair[i+1] == 2){cout <<"B";}
      if(chair[i+1] == 3){cout <<"C";}
      if(chair[i+1] == 4){cout <<"D";}
    }
    cout <<endl;
  }
  return 0;
}