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[:len(chair)-1], ""))
	}
}

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<vector>
#include<algorithm>
using namespace std;
void A(vector<char>&);
void B(vector<char>&);
void C(vector<char>&);
void D(vector<char>&);
char get(vector<char>&, bool, int);
int main() {
	int n, m;
	while (cin >> n >> m&&n != 0) {
		vector<char> line(n + 1, '#');
		for (int i = 0; i < m; ++i) {
			char num;
			cin >> num;
			if (num == 'A') {
				A(line);
			}
			else if (num == 'B') {
				B(line);
			}
			else if (num == 'C') {
				C(line);
			}else{
				D(line);
			}
		}
		for (int i = 1; i < line.size(); ++i) {
			cout << line[i];
		}
		cout << endl;
	}
	return 0;
}

char get(vector<char>&line, bool right, int place) {
	if (right) {
		if (place == line.size() - 1)return '#';
		else return line[place + 1];
	}
	else {
		return line[place - 1];
	}
}

void A(vector<char> &line) {
	for (int i = 1; i < line.size(); ++i) {
		if (line[i] == '#') {
			line[i] = 'A';
			break;
		}
	}
}

void B(vector<char> &line) {
	for (int i = line.size() - 1; i > 0; --i) {
		if (line[i] == '#'&&get(line, true, i) != 'A' && get(line, false, i) != 'A') {
			line[i] = 'B';
			return;
		}
	}
	for (int i = 1; i < line.size(); ++i) {
		if (line[i] == '#') {
			line[i] = 'B';
			return;
		}
	}
}

void C(vector<char> &line) {
	for (int i = 1; i < line.size(); ++i) {
		if (line[i] != '#') {
			if (i != line.size() - 1 && line[i + 1] == '#') {
				line[i + 1] = 'C';
				return;
			}
			else if (i != 1 && line[i - 1] == '#') {
				line[i - 1] = 'C';
				return;
			}
		}
	}
	if (line.size() % 2 == 0) {
		line[line.size() / 2] = 'C';
		return;
	}
	else {
		line[line.size() / 2 + 1] = 'C';
	}
}

void D(vector<char> &line) {
	vector<int> dline(line.size());
	int num = line.size() + 1;
	bool flag = false;
	for (int i = 1; i < line.size(); ++i) {
		++num;
		if (line[i] != '#') {
			num = 0;
			flag = true;
		}
		dline[i] = num;
	}
	if (!flag) {
		line[1] = 'D';
		return;
	}
	num = line.size() + 1;
	for (int i = line.size() - 1; i > 0; --i) {
		++num;
		if (line[i] != '#') {
			num = 0;
		}
		dline[i] = min(dline[i], num);
	}
	int mn = 0, mp = 0;
	for (int i = 1; i < line.size(); ++i) {
		if (mn < dline[i]) {
			mn = dline[i];
			mp = i;
		}
	}
	line[mp] = 'D';
}

C++: #include <bits/stdc++.h>
using namespace std;
int n,m;
char chair[200];

void A(char ch){
  int i=1;
  while(chair[i]!='#') i++;
  chair[i]=ch;
}

void B(){
  int i=n;
  while(chair[i]!='#')i--;
  chair[i]='B';
}

void C(int kai){
  if(kai==0){
    if(n%2)chair[(n+1)/2]='C';
    else chair[n/2+1]='C';
    return;
  }
  int f=1;
  for(int i=1;i<=n;i++){
    if(chair[i]=='#')continue;
    if(chair[i+1]=='#') chair[i+1]='C',i=n,f=0;
    else if(chair[i-1]=='#') chair[i-1]='C',i=n,f=0;
   
  }
    assert(f);
}

void D(){
  int R=0,L=0;
  while(chair[n-R]=='#')R++;
  while(chair[L+1]=='#')L++;
  
  int M=0,idx=0,cnt=0;
  for(int i=1;i<=n;i++){
    if(chair[i]=='#')cnt++;
    else cnt=0;
    if(M+M%2<cnt) M=cnt,idx=i;
  }
  if(M<=2&&L<=1&&R<=1) A('D');
  else if(L-1>=(M-1)/2&&L-1>=R-1)chair[1]='D';
  else if(R-1>(M-1)/2)chair[n]='D';
  else chair[(idx-M+1)+(M-1)/2]='D';

}

int main(){
  while(1){
    cin>>n>>m;
    if(!n&&!m)break;
    memset(chair,'#',sizeof(chair));
    chair[0]=chair[n+1]=0;
    for(int i=0;i<m;i++){
      char a;
      cin>>a;
      if(a=='A') A(a);
      if(a=='B') B();
      if(a=='C') C(i);
      if(a=='D') D();
    }
    int cnt=0;
    for(int i=1;i<=n;i++) if(chair[i]!='#') cnt++;
    assert(cnt==m);
    printf("%s\n",chair+1);
  }
  return 0;
}

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

int main(){

  int n,m;
  int j;
  char chair[100];
  char p;
  int left,max,m_left;

  while(1){

    cin >> n >> m;
    if(n==0 && m==0)
      break;

    for(int i=0; i<n; i++)
      chair[i]='#';


    for(int i=0; i<m; i++){

    cin >> p;

    if(p=='A'){
      j=0;
      while(chair[j]!='#')
	j++;

      chair[j]='A';
    }///////////////////////A

    else if(p=='B'){
      j=n-1;
      while(1){
	if(chair[j]=='#'){
	  if(j==n-1 && chair[j-1]!='A')
	    break;

	  else if(j>0 && chair[j+1]!='A' && chair[j-1]!='A')
	    break;

	  else if(chair[j+1]!='A')
	    break;
	  
	  else if(j==0){
	    j=-1;
	    break;
	  }
	}
	j--;
      }

      if(j!=-1)
	chair[j]='B';

      else{
	j=0;
	while(chair[j]!='#')
	  j++;

	chair[j]='B';
      }

    }////////////////////////B


    else if(p=='C'){
      j=0;
      while(1){
	if(chair[j]!='#'){
	  if(chair[j+1]=='#'&&j!=n-1){
	    j++;
	    break;
	  }
	  else if(j!=0 && chair[j-1]=='#'){
	    j--;
	    break;
	  }
	}

	if(j==n-1){
	  j=-1;
	  break;
	}

	j++;
      }

      if(j==-1){
	if(n%2==1)
	  j=(n+1)/2;
	else
	  j=n/2+1;
      }

      chair[j] = 'C';
    }///////////////////////C


    else{
      left=0; max=1; m_left=0;
      j=1;
      while(j<=n-1){
	if(chair[j]!='#'){
	  left=j;

	  j++;
	}

	if(max < j-left){
	  max = j-left;
	  m_left = left;
	}

	j++;
      }

      if(max <= 2){
	j=0;
	while(j<n && chair[j] != '#')
	  j++;
      }

      else if(max == n-1)
	j=0;

      else{
	if(max%2==1)
	  j=m_left+max/2 +1;
	else
	  j=m_left+max/2;
      }


      chair[j]='D';

    }///////////////////////D

    }


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


    cout << endl;

  }


  return 0;

}