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>
#include <vector>
#include <algorithm>

using namespace std;

int main(){

	int n,m;
	bool en=false;
	while(cin>>n>>m&&!(n==0&&m==0)){
		if(!en)
			en=true;
		else
			cout<<endl;

		char chair[101];
		char ch;
		fill(chair,chair+101,'#');
		for(int i = 0; i < m; i++){
			cin>>ch;
			if(ch=='A'){
				for(int j = 0; j < n; j++){
					if(chair[j]=='#'){
						chair[j]=ch;
						break;
					}
				}
			}
			else if(ch=='B'){
				bool f=false;
				for(int j = n-1; j >=0; j--){
					if(chair[j]=='#'&&((j-1<0||chair[j-1]!='A')&&(j+1>=n||chair[j+1]!='A'))){
						chair[j]=ch;
						f=true;
						break;
					}
				}
				// ÀêÈ©Á½ê
				if(!f){
					for(int j = 0; j < n; j++){
						if(chair[j]=='#'){
							chair[j]=ch;
							break;
						}
					}
				}
			}
			else if(ch=='C'){
				bool f=false;
				for(int j = 0; j < n; j++){
					if(chair[j]!='#'){
						f=true;
						break;
					}
				}
				if(!f){
					chair[n/2]==ch;
				}
				else{
					for(int j = 0; j < n; j++){
						if(chair[j]!='#'){
							if(j+1<n&&chair[j+1]=='#'){
								chair[j+1]=ch;
								f=true;
								break;
							}
							else if((j-1>=0)&&chair[j-1]=='#'){
								chair[j-1]=ch;
								f=true;
								break;
							}
						}
					}
				}
			}
			else if(ch=='D'){
				int dists[101];
				fill(dists,dists+101,1000000);
				bool fff=false;
				for(int j = 0; j < n; j++){
					if(chair[j]!='#'){
						fff=true;
						break;
					}
				}
				if(fff==false){
					chair[0]=ch;
				}
				else{
					for(int j = 0; j < n; j++){
						if(chair[j]!='#'){
							for(int k = 0; k < n; k++){
								dists[k]=min(dists[k],abs(j-k));
							}
						}
					}
					int minCost=1000000;
					int idx;
					for(int j = 0; j < n; j++){
						if(chair[j]=='#'){
							if(minCost>dists[j]){
								minCost=dists[j];
								idx=j;
							}
						}
					}
					chair[idx]=ch;
				}
			}
		}
		for(int i = 0; i < n; i++){
			cout<<chair[i];
		}
	}

	return 0;
}

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

int N;
int table[128];

void doA() {
  for(int i = 0; i < N; i++) if( table[i] == '#' ) {
      table[i] = 'A';
      return;
    }
}

void doB() {
  for(int i = N - 1; i >= 0; i--) {

    if( table[i] == '#' ) {
      
      bool a = false;
      if( i - 1 >= 0 && table[i - 1] == 'A' ) a = true;
      if( i + 1 < N && table[i + 1] == 'A' ) a = true;
      
      if( ! a ) {
        table[i] = 'B';
        return;
      }
    }    
  }

  for(int i = 0; i < N; i++) if( table[i] == '#' ) {
      table[i] = 'B';
      return;
    }

}

void doC() {
  for(int i = 0; i < N; i++) {
    if( table[i] != '#' ) {
      if( i + 1 < N && table[i + 1] == '#' ) {
        table[i + 1] = 'C'; return;
      }

      if( i - 1 < N && table[i - 1] == '#' ) {
        table[i - 1] = 'C'; return;
      }

    }
  }

  if( N & 1 ) table[(N + 1) / 2 - 1] = 'C';
  else table[N / 2] = 'C';
}

void doD() {
  static int temp[128];
  for(int i = 0; i < 128; i++) temp[i] = 987654321;
  
  for(int i = 0; i < N; i++) {
    if( table[i] != '#' ) 
      temp[i] = -1;
    else 
      for(int j = 0; j < N; j++) 
        if( table[j] != '#' ) {
          temp[i] = min( temp[i], abs(i - j));
        }
  }
  
  int best = 0;
  for(int i = 0; i < N; i++) 
    if( temp[best] < temp[i] )
      best = i;
  
  table[best] = 'D';
}

int main() {
  for(int M; cin >> N >> M, (N || M); ) {

    for(int i = 0; i < N; i++) table[i] = '#';

    for(int m = 0; m < M; m++) {
      char ch; cin >> ch;
      if( ch == 'A' ) doA();
      if( ch == 'B' ) doB();
      if( ch == 'C' ) doC();
      if( ch == 'D' ) doD();
    }
    for(int i = 0; i < N; i++) cout << (char)(table[i]); cout << endl;
  }
}