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<algorithm>
const int infty = 1<<28;
using namespace std;
int main()
{
  while(true){
    int n,m;
    cin >> n >> m;
    if( n == 0 && m == 0 ) break;
    char C[n+2];
    fill(C,C+n+2,'#');

    cout << " ---------- " << endl;
    for(int p = 0; p < m; ++p){
      char c;
      cin >> c;
      for(int i = 1; i < 1+n; ++i){
	cout << C[i];
      }
      cout << endl;

      if(c=='A'){
	for(int i = 1; i < 1+n; ++i){
	  if( C[i] == '#' ){
	    C[i] = 'A';
	    break;
	  }
	}
      }else if(c=='B'){
	bool sc=false;
	for(int i = n; i >= 1; --i){
	  if( C[i] == '#' && C[i-1] != 'A' && C[i+1] != 'A' ){
	    C[i] = 'B';
	    sc=true;
	    break;
	  }
	}
	if(!sc){
	  for(int i = 1; i < n+1; ++i){
	    if( C[i] == '#' ){
	      C[i] = 'B';
	      break;
	    }
	  }
	}
      }else if(c=='C'){
	bool sc = false;
	for(int i = 1; i < 1+n; ++i){
	  if( C[i] != '#' ){
	    if( C[i+1] != '#' ){
	      if( C[i-1] != '#' ){
		continue;
	      }else{
		C[i-1] = 'C';
		sc=true;
		break;
	      }
	    }else{
	      C[i+1] = 'C';
	      sc=true;
	      break;
	    }
	  }
	}
	if( !sc ){
	  if( n % 2 == 0 ){
	    C[ n/2 + 1 ] = 'C';
	  }else{
	    C[ (n+1)/2 ] = 'C';
	  }
	}
      }else if(c=='D'){
	int max_dist = -1;
	int nearest_dist[n+2];
	fill(nearest_dist,nearest_dist+n+2,infty);
	bool empty=true;
	for(int i = 1; i < 1+n; ++i){
	  if( C[i] != '#' ) empty=false;
	}
	if(empty){C[1]='D';continue;}
	
	for(int i = 1; i < 1+n; ++i){
	  if( C[i] != '#' ) continue;
	  int min_right = infty, min_left = infty;
	  for(int j = i - 1; j >= 1; --j){
	    if( C[j] != '#'){
	      min_left = i - j - 1;
	      break;
	    }
	  }
	  for(int j = i + 1; j < 1+n; ++j){
	    if( C[j] != '#' ){
	      min_right = j - i - 1;
	      break;
	    }
	  }

	  nearest_dist[i] = min( min_right, min_left );
	  max_dist = max( max_dist, nearest_dist[i] );
	}
	for(int i = 1; i < i+n; ++i){
	  //cout << nearest_dist[i] << ' ' << max_dist << endl;
	  if( nearest_dist[i] == max_dist ){
	    C[i] = 'D';
	    break;
	  }
	}
      }
    }
    for(int i = 1; i < 1+n; ++i){
      cout << C[i];
    }
    cout << endl;
  }
  return 0;
}

C++: #include <string>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
void solve1(string& s, char c) {
	s[s.find('#')] = c;
}
void solve2(string& s) {
	for (int i = s.size() - 1; i >= 0; i--) {
		if (s[i] == '#' && (i < s.size() - 1 && s[i + 1] != 'A') && (i > 0 && s[i - 1] != 'A')) {
			s[i] = 'B'; return;
		}
	}
	solve1(s, 'B');
}
vector<int> dist(string s) {
	vector<int> ret(s.size(), 999999999);
	for (int i = 0; i < s.size(); i++) {
		if (s[i] != '#') {
			for (int j = 0; j < s.size(); j++) {
				ret[j] = min(ret[j], abs(i - j));
			}
		}
	}
	return ret;
}
void solve3(string &s) {
	for (int i = 0; i < s.size(); i++) {
		if (s[i] != '#') {
			if (i < s.size() - 1 && s[i + 1] == '#') {
				s[i + 1] = 'C'; return;
			}
			if (i > 0 && s[i - 1] == '#') {
				s[i - 1] = 'C'; return;
			}
		}
	}
	if (s.size() % 2 == 1) s[(s.size() - 1) / 2] = 'C';
	else s[s.size() / 2] = 'C';
}
void solve4(string &s) {
	vector<int> ret = dist(s);
	s[max_element(ret.begin(), ret.end()) - ret.begin()] = 'D';
}
int N, Q;
int main() {
	while (cin >> N >> Q, N) {
		string s(N, '#'), t;
		while (Q--) {
			cin >> t;
			if (t == "A") solve1(s, 'A');
			if (t == "B") solve2(s);
			if (t == "C") solve3(s);
			if (t == "D") solve4(s);
		}
		cout << s << endl;
	}
	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;
}