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<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<cassert>
#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<numeric>
#include<algorithm>
#include<bitset>
#include<complex>

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
#define mp make_pair

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cout << *i << " "; cout << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

int chairs[110];
int n,m;

void fa(){
	int i;
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			chairs[i]=1;
			return;
		}
	}
}

void fb(){
	int i;
	for(i=n-1;i>=0;i++){
		if(chairs[i]==0&&(i==n-1||chairs[i+1]!=1)&&(i==0||chairs[i-1]!=1)){
			chairs[i]=2;
			return;
		}
	}
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			chairs[i]=2;
			return;
		}
	}
}

void fc(){
	int i;
	for(i=0;i<n;i++){
		if(chairs[i]==0)continue;
		if(i!=n-1&&chairs[i+1]==0){
			chairs[i+1]=3;
			return;
		}
		if(i!=0&&chairs[i-1]==0){
			chairs[i-1]=3;
			return;
		}
	}
	if(n%2==0){
		chairs[n/2+1]=3;
		return;
	}else{
		chairs[(n+1)/2]=3;
		return;
	}
}

void fd(){
	int i,j;
	int c=0,d=0,dd;
	for(i=0;i<n;i++){
		if(chairs[i]==0){
			for(j=1;i-j>=0;j++){
				if(chairs[i-j]!=0)break;
			}
			if(i-j<0)j=n;
			dd=j;
			for(j=1;i+j<n;j++){
				if(chairs[i+j]!=0)break;
			}
			if(i+j==n)j=n;
			chmin(dd,j);
			if(d<dd){
				c=i;
				d=dd;
			}
		}
	}
	chairs[c]=4;
	return;
}

int main() {
	while(cin>>n>>m){
		int i;
		string str;
		for(i=0;i<n;i++)chairs[i]=0;
		for(i=0;i<m;i++){
			cin>>str;
			if(str[0]=='A')fa();
			if(str[0]=='B')fb();
			if(str[0]=='C')fc();
			if(str[0]=='D')fd();
		}
		for(i=0;i<n;i++){
			if(chairs[i]==0)cout<<"#";
			else if(chairs[i]==1)cout<<"A";
			else if(chairs[i]==2)cout<<"B";
			else if(chairs[i]==3)cout<<"C";
			else if(chairs[i]==4)cout<<"D";
		}
		cout<<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#define MAX 100

using namespace std;

int n,m;
char chair[MAX+1];

void A(){
  for(int i = 0 ; i < n ; i++){

    if(chair[i] == '#'){
      chair[i] = 'A';
      return;
    }

  }
}

void B(){
  int found = -1;

  for(int i = 0 ; i < n ; i++){
    if(chair[i] == 'A'){
      found = i;
    }
  }

  if(found == -1){
    for(int i = n-1 ; i >= 0 ; i--){

      if(chair[i] == '#'){
	chair[i] = 'B';
	return;
      }

    }

  }
  else{
    for(int i = n-1 ; i >= 0 ; i--){

      if(chair[i] == '#'){	
	if(i && chair[i-1] == 'A') continue;
	if(i != n-1 && chair[i+1] == 'A') continue;
	chair[i] = 'B';
	return;
      }

    }

    for(int i = 0 ; i < n ; i++){
      if(chair[i] == '#'){
	chair[i] = 'B';
	return;
      }
    }

  }

}

void C(){
  int cnt = count(chair,chair+n,'#');

  if(cnt == n){
    if(n % 2){
      chair[(n+1)/2] = 'C';
    }
    else{
      chair[n/2+1] = 'C';
    }
    return;
  }
  else{
    for(int i = 0 ; i < n ; i++){

      if(chair[i] != '#'){

	if(i != n-1 && chair[i+1] == '#'){
	  chair[i+1] = 'C';
	  return;
	}
	else{
	  if(i && chair[i-1] == '#'){
	    chair[i-1] = 'C';
	    return;
	  }
	}

      }

    }
  }

}

void D(){
  int Breadth = 0,pos;

  for(int i = 0 ; i < n ; i++){
    int dist = (1<<29);
    for(int j = 0 ; j < n ; j++){
      if(chair[j] != '#'){
	dist = min(dist,abs(i-j));
      }
    }
    if(Breadth < dist){
      Breadth = dist;
      pos = i;
    } 
  }

  chair[pos] = 'D';
}

int main(){
  while(cin >> n >> m , n | m){
    char person;
    
    for(int i = 0 ; i < n ; i++)
      chair[i] = '#';

    for(int i = 0 ; i < m ; i++){
      cin >> person;
      
      switch(person){
      case 'A':	
	A(); 
	break;
      case 'B': 
	B(); 
	break;
      case 'C': 
	C(); 
	break;
      case 'D': 
	D(); 
	break;
      }

    }

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

  return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
vector<int> data;
int n,N;

int getLeft(){
	rep(i,n)if(data[i] == 0)return i;
	rep(i,n)cout << data[i] << " ";cout << endl;
	return -1;
}

int B(){
	for(int i=n-1;i>=0;i--){
		if(data[i] == 0 && data[i+1] != 1 && data[i-1] != 1)return i;
	}
	return getLeft();
}
int C(){
	bool f = true;
	rep(i,N)f &=(data[i+1]==0);
	if(f)return (N&1?n/2:N/2+1);
	
	rep(i,n){
		if(data[i] == 0 && data[i+1] != -1 && data[i+1])return i;
		if(data[i] == 0 && data[i-1] != -1 && data[i-1])return i;
	}
}

int most(int pos,int a){
	int i = 0;
	while(!data[pos+i*a]){
		i++;
		if(data[pos+i*a] == -1)return 999999;
	}
	return i;
}
int D(){
	int good , val = -1;
	rep(i,n){
		if(data[i] == 0){
			int t = min( most(i,-1) , most(i,1) );
			if(t > val){
				val = t;
				good = i;
			}
		}
	}
	return good;
}
int main(){
	string tab = "#ABCD";
	int m;
	while(cin >> n >> m , n ){
		N = n ; n++;
		data.resize(N+2);
		fill(data.begin(),data.end(),0);
		data[0] = -1 , data[n] = -1;
		
		rep(i,m){
			char c; cin >> c;
			switch(c){
			case 'A':
				data[getLeft()] = 1;
				break;
			case 'B':
				data[B()] = 2;
				break;
			case 'C':
				data[C()] = 3;
				break;
			case 'D':
				data[D()] = 4;
				break;
			}
		}
		rep(i,N){
			int t = data[i+1];
			cout << tab[t];
		}
		cout << endl;
	}
}