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
		}
		chair := make([]string, n+1)
		for i := range chair {
			chair[i] = "#"
		}
		chair[n] = "Sentinel"
		for i := 0; i < m; i++ {
			scanner.Scan()
			switch who := scanner.Text(); who {
			case "A": // 左から眺めて行って空いている席があったら即座に座る
				for j := 0; j < n; j++ {
					if chair[j] == "#" {
						chair[j] = "A"
						break
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "B":
				flag := true
				// 右端からAの隣でない席を探していく
				for j := n-1; j > -1; j-- {
					if chair[j] == "#" && (j == 0 || chair[j-1] != "A") && chair[j+1] != "A" {
						flag = false
						chair[j] = "B"
						break
					}
				}
				// Aの隣しか空いていないので一番左端の空いている席に座る
				if flag {
					for j := 0; j < n; j++ {
						if chair[j] == "#" {
							chair[j] = "B"
							break
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "C":
				if i == 0 {
					chair[n/2] = "C" // 先客が誰もいないときは真ん中の椅子に座る
				} else {
					for j := 0; j < n; j++ { // 左から舐めて
						if chair[j] != "#" { // その席が空いていなくて
							if chair[j+1] == "#" { // 右隣が空いているなら座る
								chair[j+1] = "C"
								break
							} else if j != 0 && chair[j-1] == "#" { // 右隣が空いていないので左隣に座る
								chair[j-1] = "C"
								break
							}
						}
					}
				}
				// log.Println(chair)
				break // 次の人を読み込む
			case "D":
				distanceTable := make([]int ,n)
				for j := range distanceTable {
					distanceTable[j] = INF
				}
				for j:= 0; j < n; j++ {
					if chair[j] != "#" {
						for k := 0; k < n; k++ {
							distanceTable[k] = min(distanceTable[k], abs(j-k))
						}
					}
				}
				// log.Println("distanceTAble:", distanceTable)
				at := 0
				distance := 0
				for j := 0; j < n; j++ {
					if distance < distanceTable[j] {
						at = j
						distance = distanceTable[j]
					}
				}
				chair[at] = "D"
				// log.Println(chair)
				break // 次の人を読み込む
			}
		}
		fmt.Println(strings.Join(chair, ""))
	}
}

func min(a, b int) int {
	if a > b {
		return b
	}
	return a
}

func abs(a int) int {
	if a < 0 {
		return -a
	}
	return a
}

C++: #include<stdio.h>
#include<string.h>
#include<math.h>
int main(void)
{
	int a,s,d[101],f,g,h,i,j,aa,k,ss,dd,ff,gg,xx,cc;
	char z[2];
	while(1){
		scanf("%d %d",&a,&s);
		if(a==0&&s==0) break;
		for(i=0;i<a;i++) d[i]=0;
		for(i=0;i<s;i++){
			scanf("%s",z);
			if(z[0]=='A'){
				for(j=0;j<a;j++){
					if(d[j]==0){
						d[j]=1;
						break;
					}
				}
			}
			else if(z[0]=='B'){
				aa=0;
				for(j=a-1;j>=0;j--){
					if(d[j]==0){
						if(j==a-1){
							if(d[j-1]!=1){
								d[j]=2;
								aa=1;
								break;
							}
						}
						else if(j==0){
							if(d[1]!=1){
								d[j]=2;
								aa=1;
								break;
							}
						}
						else{
							if(d[j-1]!=1&&d[j+1]!=1){
								d[j]=2;
								aa=1;
								break;
							}
						}
					}
				}
				if(aa==0){
					for(j=0;j<a;j++){
						if(d[j]==0){
							d[j]=2;
							break;
						}
					}
				}
			}
			else if(z[0]=='C'){
				aa=0;
				for(j=0;j<a;j++){
					if(d[j]!=0){
						aa=1;
						break;
					}
				}
				if(aa==0) d[a/2]=3;
				else if(aa==1){
					for(j=0;j<a;j++){
						if(d[j]!=0){
							if(j!=0&&d[j-1]==0){
								d[j-1]=3;
								break;
							}
							else if(d[j+1]==0){
								d[j+1]=3;
								break;
							}
						}
					}
				}
			}
			else if(z[0]=='D'){
				aa=0;
				ss=0;
				ff=0;
				gg=0;
				for(j=0;j<a;j++){
					if(d[j]!=0){
						gg=1;
						break;
					}
				}
				if(gg==0) d[0]=4;
				else{
					for(j=a-1;j>=0;j--){
						dd=0;
						xx=0;
						if(d[j]==0){
							ss=j;
							for(k=j;k>=0;k--){
								if(k==a-1) xx=2;
								if(d[k]!=0){
									break;
								}
								if(k==0) xx=1;
								dd++;
							}
						}
						if(xx==2&&aa<=dd){
							aa=dd;
							ff=ss;
							cc=1;
						}
						if(xx==1&&aa<=dd){
							aa=dd;
							ff=ss;
							cc=2;
						}
						if(xx==0&&aa<=dd/2){
							aa=dd/2;
							ff=ss;
							cc=0;
						}
					}
					if(cc==2) d[0]=4;
					if(cc==1) d[aa]=4;
					if(cc==0) d[ff-aa]=4;
				}
			}
		}
		for(i=0;i<a;i++){
			if(d[i]==0) printf("#");
			else if(d[i]==1) printf("A");
			else if(d[i]==2) printf("B");
			else if(d[i]==3) printf("C");
			else if(d[i]==4) printf("D");
		}
		printf("\n");
	}
	return 0;
}

C++: #include <iostream>
#include <complex>
#include <sstream>
#include <string>
#include <algorithm>
#include <deque>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <vector>
#include <set>
#include <limits>
#include <cstdio>
#include <cctype>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
#define REP(i, j) for(int i = 0; i < (int)(j); ++i)
#define FOR(i, j, k) for(int i = (int)(j); i < (int)(k); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define REVERSE(v) reverse((v).begin(), (v).end())
typedef complex<double> P;

int N, M;

void check(vector<char> &v, char c){
  if(N == 1) { v[0] = c; return ; }
  if(c == 'A'){
    REP(i, v.size()) if(v[i] == '#'){ v[i] = c; return ; }
  }
  if(c == 'B'){
    if(v[N - 1] == '#' && v[N - 2] != 'A') { v[N - 1] = c; return ; }
    for(int i = N - 2; i > 1; i--) if(v[i] == '#' && v[i - 1] != 'A' && v[i + 1] != 'A') { v[i] = c; return ; }
    if(v[0] == '#' && v[1] != 'A') { v[0] = c; return ; }
    REP(i, v.size()) if(v[i] == '#'){ v[i] = c; return ; }
  }
  if(c == 'C'){
    if(v[0] != '#' && v[1] == '#') { v[1] = c; return ; }
    for(int i = 1; i < N - 1; i++){
      if(v[i] != '#' && v[i + 1] == '#') { v[i + 1] = c; return ; }
      if(v[i] != '#' && v[i - 1] == '#') { v[i - 1] = c; return ; }
    }
    if(v[N - 1] != '#' && v[N - 2] == '#') { v[N - 2] = c; return ; }
    if(N % 2) { v[(N + 1) / 2 - 1] = c; return ; }
    v[N / 2] = c;
  }
  if(c == 'D'){
    vector<int> d(N, 1e9);
    REP(i, N){
      if(v[i] == '#') continue;
      d[i] = 0;
      for(int j = i + 1, cnt = 1; j < N; ++j, ++cnt) d[j] = min(d[j], cnt);
      for(int j = i - 1, cnt = 1; j >= 0; --j, ++cnt) d[j] = min(d[j], cnt);
    }
    int tar = 0;
    REP(i, N) tar = max(tar, d[i]);
    if(tar == N) { v[0] = c; return ; }
    REP(i, N) if(d[i] == tar) { v[i] = c; return ; }
  }
}

int main() {
  while(cin >>N >>M && N && M){
    vector<char> v(N, '#');
    REP(i, M){
      char c; cin >>c;
      check(v, c);
    }
    REP(i, N) cout <<v[i]; cout <<endl;
  }
  return 0;
}

C++: #include <iostream>
using namespace std;
void solve(int n,int m){
	string s,a;
	int pos,temp,now;
	bool f,ok;
	for(int i=0;i<n;i++)s.push_back('#');
	for(int x=0;x<m;x++){
		cin>>a;
		if(a[0]=='A'){
			for(int i=0;i<n;i++)if(s[i]=='#'){
				s[i]='A';
				break;
			}
		}
		else if(a[0]=='B'){
			ok=false;
			for(int i=n-1;i>=0;i--)if(s[i]=='#'){
				f=true;
				if(i<n-1){
					if(s[i+1]=='A')f=false;
				}
				if(i>0){
					if(s[i-1]=='A')f=false;
				}
				if(f){
					s[i]='B';
					ok=true;
					break;
				}
			}
			if(!ok)for(int i=0;i<n;i++)if(s[i]=='#'){
				s[i]='B';
				break;
			}
		}
		else if(a[0]=='C'){
			if(x==0)s[n/2]='C';
			else{
				for(int i=0;i<n;i++)if(s[i]!='#'){
					if(i<n-1&&s[i+1]=='#'){
						s[i+1]='C';
						break;
					}
					else if(i>0&&s[i-1]=='#'){
						s[i-1]='C';
						break;
					}
				}
			}
		}
		else{
			if(x==0)s[0]='D';
			else{
				pos=temp=now=0;
				for(int i=0;i<n;i++){
					if(s[i]=='#'){
						temp=n;
						for(int j=i-1;j>=0;j--){
							if(s[j]!='#'){
								temp=i-j;
								break;
							}
						}
						for(int j=i+1;j<n;j++){
							if(s[j]!='#'){
								if(j-i<temp)temp=j-i;
								break;
							}
							
						}
						if(temp>now){
							now=temp;
							pos=i;
						}
					}
				}
				s[pos]='D';
			}
		}
	}
	cout<<s<<endl;
}
int main(){
	int n,m;
	while(true){
		cin>>n>>m;
		if(n==0&&m==0)break;
		solve(n,m);
	}
}