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 <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>
using namespace std;

#define MAX 110
typedef pair<int, int> P;
int n, m;
char chair[MAX];
bool isZero;

bool isCanSit(int x){
  if(chair[x] == '#') return true;
  return false;
}

void A(){
  for(int i = 0 ; i < n ; i++){
    if(isCanSit(i)){
      chair[i] = 'A';
      isZero = false;
      return;
    }
  }
}

bool isNext(int x){
  if(chair[x-1] == 'A' || chair[x+1] == 'A') return true;
  return false;
}

void B(){
  for(int i = n-1 ; i >= 0 ; i--){
    if(isCanSit(i) && !isNext(i)){
      chair[i] = 'B';
      isZero = false;
      return;
    }
  }
  
  for(int i = 0 ; i < n ; i++){
    if(isCanSit(i)){
      chair[i] = 'B';
      isZero = false;
      return;
    }
  }
}


void C(){
  if(isZero){
    chair[n/2] = 'C';
    isZero = false;
    return;
  }
  
  for(int i = 0 ; i < n ; i++){
    if(!isCanSit(i)){
      if(isCanSit(i+1)){
	if(i+1 != n){
	  chair[i+1] = 'C';
	  isZero = false;
	  return;
	}
	else{
	  chair[i-1] = 'C';
	  isZero = false;
	  return;
	}
      }
      else if(isCanSit(i-1)){
	chair[i-1] = 'C';
	isZero = false;
	return;
      }
    }
  }
}

bool DcanSitNoneNext(int x){
  if(x == n-1){
    if(chair[x-1] == '#') return true;
  }
  if(x == 0){
    if(chair[x+1] == '#') return true;
 }  
  if(chair[x-1] == '#' && chair[x+1] == '#') return true;
  return false;
}

int calcDisD(int x){
  int ret, cnt = 0;
  for(int i = x-1 ; i >= 0 ; i--){ // left
    if(chair[i] != '#') break;
    else cnt++;
  }
  
  ret = cnt;
  cnt = 0;
  
  for(int i = x+1 ; i < n ; i++){ // right
    if(chair[i] != '#') break;
    else cnt++;
  }
  
  ret = max(ret, cnt);
  return ret;
}

void D(){
  if(isZero){
    chair[0] = 'D';
    isZero = false;
    return;
  }
  
  int sit;
  int dis[MAX];
  fill(dis, dis+MAX, MAX);
  for(int i = 0 ; i < n ; i++){
    if(chair[i] != '#'){
      for(int j = 0 ; j < n ; j++){
	dis[j] = min(dis[j], abs(i-j));
      }
    }
  }  
  int d = 0;
  for(int i = 0 ; i < n ; i++){
    if(dis[i] > d){
      sit = i;
      d = dis[i];
    }
  }
  chair[sit] = 'D';
  return;
}
  
void init(){
  fill(chair, chair+MAX, '#');
  isZero = true;
}

void display(){
  for(int i = 0 ; i < n ; i++){
    cout << chair[i];
  }
  cout << endl;
}

int main(){
  char p;
  while(cin >> n >> m){
    if(n == 0 && m == 0) break;
    init();
    for(int i = 0 ; i < m ; i++){
      cin >> p;
      if(p == 'A') A();
      if(p == 'B') B();
      if(p == 'C') C();
      if(p == 'D') D();
      //      display();
    }
    display();
  }
  return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) REP((i),0,(n))
#define RREP(i,a,b) for(int i=(int)(a);i>=(int)(b);i--)
#define rrep(i,n) RREP(i,n,0)
#define each(it,X) for(__typeof((X).begin())  it=(X).begin();it!=(X).end();it++)
#define all(v) ((v).begin(),(v).end())
#define fi first
#define se second
#define pb push_back
typedef pair<int,int>pr;
typedef vector<int>vi;
typedef vector<vi>vvi;
typedef set<int>si;
const int INF=1070000000ll;
const int mod=1000000007ll;

int n,m;
char seet[100];
void A(){
    rep(i,n)if(seet[i]=='#'){
        seet[i]='A';
        return;
    }
}
void B(){
    rrep(i,n-1)if(seet[i]=='#'){
        if((i!=0||seet[i-1]!='A')&&(i!=n-1||seet[i+1]!='A')){
            seet[i]='B';
            return;
        }
    }
    rep(i,n)if(seet[i]=='#'){
        seet[i]='B';
        return;
    }
}
void C(){
    rep(i,n)if(seet[i]!='#'){
        if(i!=n-1&&seet[i+1]=='#'){
            seet[i+1]='C';return;
        }
        if(i!=0&&seet[i-1]=='#'){
            seet[i-1]='C';return;
        }
    }
    seet[n/2]='C';
}
void D(){
    int ma=0,dist=0;
    rep(i,n)if(seet[i]=='#'){
        int v=1000;
        rep(j,n)if(seet[j]!='#'){
            v=min(abs(i-j),v);
        }
        if(dist<v){
            dist=v;
            ma=i;
        }
    }
    seet[ma]='D';
}
signed main(){
    cin.tie(0);ios_base::sync_with_stdio(0);

    while(cin>>n>>m,n||m){
        fill_n(seet,n,'#');
        rep(i,m){
            char c;cin>>c;
            switch(c){
                case 'A':A();break;
                case 'B':B();break;
                case 'C':C();break;
                case 'D':D();break;
            }
        }
        rep(i,n)cout<<seet[i];cout<<endl;
    }
    return 0;
}