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[100],f,g,h,i,j,k,c,x[3],o;
	char z[2];
	while(1){
		scanf("%d %d",&a,&s);
		if(a==0&&s==0) break;
		f=a;
		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;
						f--;
						break;
					}
				}
			}
			else if(z[0]=='B'){
				g=0;
				for(j=a-1;j>=0;j--){
					if(d[j]==0&&d[j+1]!=1&&d[j-1]!=1){
						d[j]=2;
						f--;
						break;
					}
					if(d[j]==0) g++;
					if(f==g){
						d[j]=2;
						f--;
						break;
					}
				}
			}
			else if(z[0]=='C'){
				if(a==f){
					if(a%2==1){
						d[((a+1)/2)-1]=3;
						f--;
					}
					else if(a%2==0){
						d[a/2]=3;
						f--;
					}
				}
				else if(a>f){
					for(j=0;j<a;j++){
						if(d[j]>0){
							if(d[j+1]==0&&j+1<a){
								d[j+1]=3;
								f--;
								break;
							}
							else if(d[j-1]==0&&j-1>=0){
								d[j-1]=3;
								f--;
								break;
							}
						}
					}
				}
			}
			else if(z[0]=='D'){
				h=-1;
				c=-1;
				int v=0;
				x[0]=0;
				x[1]=0;
				for(j=a-1;j>=0;j--){
					if(d[j]>0&&v==0){
						h=j;
						if(d[0]==0){
							x[0]=h-1;
							x[1]=0;
						}
						v=1;
					}
					else if(d[j]>0&&v==1){
						c=j;
					}
					if(c>-1&&h>-1){
						if((h-c)%2==1){
							if(x[0]<=((h-c)/2-1)){
								x[0]=(h-c)/2-1;
								x[1]=h-(h-c)/2-1;
							}
						}
						else if((h-c)%2==0){
							if(x[0]<=(h-c)/2){
								x[0]=(h-c)/2;
								x[1]=h-(h-c)/2;
							}
						}
					}
					if(c>-1) h=c;
				}
				if(d[a-1]==0){
					if(x[0]<(a-1)-c){
						x[0]=(a-1)-c;
						x[1]=a-1;
					}
				}
				if(h==-1) x[1]=0;
				else if(c==-1){
					x[0]=(a-1)-h;
					x[1]=a-1;
					if(x[0]<h) x[1]=0;
				}
				d[x[1]]=4;
				f--;
			}
		}
		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>
using namespace std;
int main(){
  while(true){
    int n,m,j;
    cin>>n>>m;
    if(!n&&!m)break;
    char seat[n];
    char seatb[n];
    int len[n];
    bool sit = false;
    for(int i=0;i<n;i++){
      seat[i] = '#';
      seatb[i] = '#';    
    }
    for(int i=0;i<m;i++){
      char p;
      cin>>p;
      if(p=='A'){
	for(j=0;j<n;j++){
	  if(seat[j]=='#'){
	    seat[j] = 'A';
	    if(j>0)seatb[j-1]=='A';
	    if(j<n-1)seatb[j+1]=='A';
	    break;
	  }
	}
	sit = true;
      }
      if(p=='B'){
	for(j=n-1;j>=0;j--){
	  if(seat[j]=='#'&&seatb[j]=='#'){
	    seat[j] = 'B';
	    break;
	  }
	}
	if(j==n){
	  for(j=0;j<n;j++){
	    if(seat[j]=='#'){
	      seat[j] = 'B';
	      break;
	    }
	  }
	}
	sit = true;
      }
      if(p=='C'){
	if(!sit){
	  seat[n/2] = 'C';
	}
	else{
	  for(j=0;j<n-1;j++){
	    if(seat[j]!='#'&&seat[j+1]=='#'){
	      seat[j+1] = 'C';
	      break;
	    }
	  }
	}
	sit = true;
      }
      if(p=='D'){
	if(!sit){
	  seat[0] = 'D';
	}
	else{
	  int l=100;
	  for(int j=0;j<n;j++){
	    if(seat[j]!='#')l = 0;
	    else l++;
	    len[j] = l;
	  }
	  l=100;
	  int lenmax = 0,maxseat;
	  for(int j=n-1;j>=0;j--){
	    if(seat[j]!='#')l = 0;
	    else l++;
	    len[j] = min(len[j],l);
	    if(lenmax<=len[j]){
	      lenmax=len[j];
	      maxseat=j;
	    }
	  }
	  seat[maxseat] = 'D';
	}
	sit = true;
      }
    }
    for(int i=0;i<n;i++)
      cout<<seat[i];
    cout<<endl;
  }
  return 0;
}