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 <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;
  }
  for(int i=1;i<=n;i++){
    if(chair[i]=='#')continue;
    if(chair[i-1]=='#') chair[i-1]='C',i=n;
    if(chair[i+1]=='#') chair[i+1]='C',i=n;
  }
}

void D(int kai){
  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');
    return;
  }
   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;
    for(int i=0;i<=130;i++) chair[i]='#';
    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(i);
    }
    printf("%s\n",chair+1);
  }
  return 0;
}

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

int main()
{
	int n,m,i,j,s[102],temp,flag,max,z,count,left,right;
	char k;
	cin>>n>>m;

	while(n!=0){

	for(i=0;i<102;i++)
		s[i]=100;
	for(i=1;i<n+1;i++)
		s[i]=0;

	for(i=0;i<m;i++){
		max=0;
		cin>>k;
		if(k=='A'){
			for(j=1;j<n+1;j++){
				if(s[j]==0){
					s[j]=1;
				break;
				}
			}
		}else if(k=='B'){
			flag=0;
			for(j=n;j>1;j--){
				if(s[j]==0){
					if(s[j+1]!=1 && s[j-1]!=1){
						s[j]=2;
						flag=1;
						break;
					}
					else temp=j;
				}
			}
			if(flag==0){
				s[j]=temp;
				temp=0;
			}
		}else if(k=='C'){
			flag = 0;
			for(j=2;j<n;j++){
				if(s[j]==0 && s[j-1]!=0){
					s[j]=3;
					flag = 1;
					break;
				}
			}
			if(flag ==0){
				if(n%2==0){
					s[n/2+1]=3;
				}
				else {
					s[(n+1)/2]=3;
				}
			}
		}
		else if(k=='D'){
			temp=0;max=0;flag=0;
			for(j=n;j>0;j--){
				if(s[j]==0){
					left=0;right=0;
					for(z=1;;z++){
						if(s[j+z]!=0)
							break;
						else
							right++;
					}

					for(z=1;;z++){
						if(s[j-z]!=0)
							break;
						else 
							left++;
					}
						if(left>right)
							 temp=left;
						else temp=right;
	
				if(temp>=max){
					max=temp;
					flag=j;
				}
				}
			}
			s[flag]=4;
		}
	}


	for(i=1;i<n+1;i++){
		if(s[i]==0)
			cout<<'#';
		else if(s[i]==1)
			cout<<'A';
		else if(s[i]==2)
			cout<<'B';
		else if(s[i]==3)
			cout<<'C';
		else if(s[i]==4)
			cout<<'D';
	}

	cout<<"\n";

	cin>>n>>m;
	}


		return 0;
	}