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[101],f,g,h,i,j,aa,k,ss,dd,ff,gg,xx,cc;
	char z[2];
	while(1){
		scanf("%d %d",&a,&s);
		if(a==0&&s==0) break;
		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;
						break;
					}
				}
			}
			else if(z[0]=='B'){
				aa=0;
				for(j=a-1;j>=0;j--){
					if(d[j]==0){
						if(j==a-1){
							if(d[j-1]!=1){
								d[j]=2;
								aa=1;
								break;
							}
						}
						else if(j==0){
							if(d[1]!=1){
								d[j]=2;
								aa=1;
								break;
							}
						}
						else{
							if(d[j-1]!=1&&d[j+1]!=1){
								d[j]=2;
								aa=1;
								break;
							}
						}
					}
				}
				if(aa==0){
					for(j=0;j<a;j++){
						if(d[j]==0){
							d[j]=2;
							break;
						}
					}
				}
			}
			else if(z[0]=='C'){
				aa=0;
				for(j=0;j<a;j++){
					if(d[j]!=0){
						aa=1;
						break;
					}
				}
				if(aa==0) d[a/2]=3;
				else if(aa==1){
					for(j=0;j<a;j++){
						if(d[j]!=0){
							if(j!=0&&d[j-1]==0){
								d[j-1]=3;
								break;
							}
							else if(d[j+1]==0){
								d[j+1]=3;
								break;
							}
						}
					}
				}
			}
			else if(z[0]=='D'){
				aa=0;
				ss=0;
				ff=0;
				gg=0;
				for(j=0;j<a;j++){
					if(d[j]!=0){
						gg=1;
						break;
					}
				}
				if(gg==0) d[0]=4;
				else{
					for(j=a-1;j>=0;j--){
						dd=0;
						xx=0;
						if(d[j]==0){
							ss=j;
							for(k=j;k>=0;k--){
								if(k==a-1) xx=2;
								if(d[k]!=0){
									break;
								}
								if(k==0) xx=1;
								dd++;
							}
						}
						//printf("%d  %d\n",j,dd);
						if(xx==2&&aa<=dd*2){
							aa=dd*2;
							ff=ss;
							cc=1;
						}
						if(xx==1&&aa<=dd*2){
							aa=dd*2;
							ff=ss;
							cc=2;
						}
						if(xx==0){
							if(aa<=dd){
								aa=dd;
								ff=ss;
								cc=0;
							//	printf("%d %d %d\n\n",ff,dd,dd/2);
							}
						}
					}
				//	printf("%d %d %d\n\n",aa,dd,cc);
					if(cc==2) d[0]=4;
					if(cc==1) d[aa/2]=4;
					if(cc==0) d[ff-(aa/2)]=4;
				}
			}
			/*for(j=0;j<a;j++){
				if(d[j]==0) printf("#");
				else if(d[j]==1) printf("A");
				else if(d[j]==2) printf("B");
				else if(d[j]==3) printf("C");
				else if(d[j]==4) printf("D");
			}
			printf("\n");*/
		}
		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 <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 <bits/stdc++.h>
using namespace std;
int n,m;
char t[120];

void A(char a){
  int i=1;
  while(t[i]!=0) i++;
  t[i]=a;
}

void B(){
  for(int i=n;i>=1;i--){
    if(t[i]==0){
      t[i]='B';
      break;
    }
  }
}

void C(int cnt){
  if(cnt==0) {
    if(n%2==0) t[n/2+1]='C';
    else t[(n+1)/2]='C';
    return;
  }


  for(int i=1;i<=n;i++){
    if(t[i]!=0&&t[i+1]==0) {
      t[i+1]='C';
      break;
    }
    if(t[i]!=0&&t[i-1]==0){
      t[i-1]='C';
      break;
    }
  }
}

void D(int cnt){
  if(cnt==0){
    t[1]='D';
    return;
  }
  int mx=0,idx=0,c=0;
  for(int i=1;i<=n;i++) {
    if(t[i]==0) c++;
    else c=0;
    if(mx+mx%2<c)mx=c,idx=i;
  }
  if(mx<c) mx=c,idx=n;
  if(mx<=2&&t[n]==0&&t[n-1]==0) {
    t[n]='D';
    return;
  }  

  if(mx<=2){
    A('D');
    return ;
  }

  if(idx==n) t[n]='D';
  else if(mx==n-1) t[1]='D';
  else   t[(idx-(idx-mx+1))/2+(idx-mx+1)]='D';
}

int main(){
  while(1){
    cin>>n>>m;
    if(!n&&!m)break;
    memset(t,0,sizeof(t));
    t[0]=t[n+1]=1;
    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);
    }

    for(int i=1;i<=n;i++)if(t[i]==0)t[i]='#';
    t[n+1]=0;
    printf("%s\n",t+1);
  }
  return 0;
}