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<iostream>
using namespace std;
int main(){
long n,m,i,j,d[101],e[101],k,dd;
char c,a[101];
while(cin>>n){
cin>>m;
if(n==0)break;
for(i=0;i<n;i++)a[i]='#';
for(j=0;j<m;j++){
cin>>c;
if(c=='A'){
for(i=0;i<n;i++)if(a[i]=='#'){a[i]='A';break;}
}else if(c=='B'){
for(i=n-1;i>=0;i--){
if(0<i&&a[i-1]!='A'&&i<n-1&&a[i+1]!='A'){a[i]='B';break;}
else if(0<i&&a[i-1]!='A'){a[i]='B';break;}
else if(i<n-1&&a[i+1]!='A'){a[i]='B';break;}
}
if(i<0){for(i=0;i<n;i++)if(a[i]=='#')a[i]='B';}
}else if(c=='C'){
for(i=0;i<n;i++){
if(a[i]!='#'){
if(i<n-1&&a[i+1]=='#'){a[i+1]='C';break;}
else if(i>0&&a[i-1]=='#'){a[i-1]='C';break;}
}
}
if(i==n)a[n/2+1]='C';
}else if(c=='D'){
for(i=0;i<n;i++)d[i]=-1;
for(i=0;i<n;i++)if(a[i]!='#')break;
if(i==n){a[0]='D';continue;}
for(;i<n;i++)if(a[i]=='#')d[i]=d[i-1]+1;else d[i]=0;
for(i=0;i<n;i++)e[i]=-1;
for(i=n-1;i>=0;i--)if(a[i]!='#')break;
for(;i>=0;i--)if(a[i]=='#')e[i]=e[i+1]+1;else e[i]=0;
for(i=0;i<n;i++)if(d[i]<e[i])d[i]=e[i];
for(k=0;k<n;k++)cout<<" "<<d[k];cout<<endl;
dd=d[n-1];
for(i=n-1;i>=0;i--)if(dd<=d[i]){dd=d[i];k=i;}
a[k]='D';
}
}
a[n]=0;cout<<a<<endl;
}
return 0;
}

C++: #include <iostream>
#include <algorithm>

using namespace std;

const int INF = 1000000000;

int n, m;
char chairs[100];
int dist[100];
int p;

bool notA(int i){
   if(i == n-1){
      return chairs[i-1] != 'A';
   }else if(i == 0){
      return chairs[i+1] != 'A';
   }else{
      return chairs[i-1] != 'A' && chairs[i+1] != 'A';
   }
}

int checkC(int idx){
   if(idx == n-1){
      if(chairs[idx-1] == '#') return -1;
      return 0;
   }else if(idx == 0){
      if(chairs[idx+1] == '#') return 1;
      return 0;
   }else{
      if(chairs[idx+1] == '#') return 1;
      if(chairs[idx-1] == '#') return -1;
      return 0;
   }
}

void setD(int idx){
   for(int i=0;idx-i>=0;i++){
      dist[idx-i] = min(dist[idx-i], i);
   }
   for(int i=0;idx+i<n;i++){
      dist[idx+i] = min(dist[idx+i], i);
   }
}

void setChar(char c){
   if(n == 1){
      chairs[0] = c;
      return;
   }
   switch(c){
      case 'A':
         for(int i=0;i<n;i++){
            if(chairs[i] == '#'){
               chairs[i] = 'A';
               setD(i);
               return;
            }
         }
         break;
      case 'B':
         for(int i=n-1;i>=0;i--){
            if(notA(i)){
               chairs[i] = 'B';
               setD(i);
               return;
            }
         }
         for(int i=0;i<n;i++){
            if(chairs[i] == '#') chairs[i] = 'B';
            cout << i << endl;
            setD(i);
            return;
         }
         break;
      case 'C':
         if(p == 0){
            if(n&1){
               chairs[(n+1)/2-1] = 'C';
               setD((n+1)/2-1);
            }else{
               chairs[n/2] = 'C';
               setD(n/2);
            }
            return;
         }
         for(int i=0;i<n;i++){
            if(chairs[i] != '#'){
               int tmp = checkC(i);
               if(tmp == 1){
                  chairs[i+1] = 'C';
                  setD(i+1);
                  return;
               }else if(tmp == -1){
                  chairs[i-1] = 'C';
                  setD(i-1);
                  return;
               }
            }
         }
         break;
      case 'D':
         int idx = 0;
         int valm = 0;
         for(int i=0;i<n;i++){
            if(dist[i] > valm){
               valm = dist[i];
               idx = i;
            }
         }
         chairs[idx] = 'D';
         setD(idx);
         break;
   }
}

main(){
   while(cin >> n >> m && (n || m)){
      fill(dist, dist+n, INF);
      fill(chairs, chairs+n, '#');
      char c;
      for(p=0;p<m;p++){
         cin >> c;
         setChar(c);
      }
      for(int i=0;i<n;i++){
         cout << chairs[i];
      }
      cout << endl;
   }
   return 0;
}

C++: #include <algorithm>
#include <cctype>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <string>
#include <vector>

using namespace std;

#define reps(i,f,n) for(int i=f; i<int(n); ++i)
#define rep(i,n) reps(i,0,n)

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;

const int INF = 1001001001;

void sit(char c, char chair[], int n)
{
	if(c == 'A'){
		rep(i, n){
			if(chair[i] == '#'){
				chair[i] = 'A';
				return;
			}
		}
	}
	else if(c == 'B'){
		int pos = -1;
		for(int i=n-1; i>=0; --i){
			if(chair[i] == '#'){
				pos = i;
				if(i!=0 && chair[i-1]=='A')
					continue;
				if(i!=n-1 && chair[i+1]=='A')
					continue;
				chair[i] = 'B';
				return;
			}
		}
		chair[pos] = 'B';
	}
	else if(c == 'C'){
		rep(i, n){
			if(chair[i] != '#'){
				if(i!=n-1 && chair[i+1]=='#'){
					chair[i+1] = 'C';
					return;
				}
				if(i!=0 && chair[i-1]=='#'){
					chair[i-1] = 'C';
					return;
				}
			}
		}
		chair[n/2] = 'C';
	}
	else{
		int B = 0;
		int Bid;
		rep(i, n){
			int dist = INF;
			rep(j, n){
				if(chair[j] != '#')
					dist = min(dist, abs(i-j));
			}
			if(dist > B){
				B = dist;
				Bid = i;
			}
		}
		chair[Bid] = 'D';
	}
}

int main()
{
	int n, m;
	while(scanf("%d%d", &n, &m), n){
		char chair[100];
		fill(chair, chair+n, '#');
		rep(i, m){
			char c;
			scanf(" %c", &c);
			sit(c, chair, n);
		}
		rep(i, n)
			putchar(chair[i]);
		puts("");
	}
	return 0;
}