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 <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>
using namespace std;

#define MAX 110
typedef pair<int, int> P;
int n, m;
char chair[MAX];
bool isZero;

bool isCanSit(int x){
  if(chair[x] == '#') return true;
  return false;
}

void A(){
  for(int i = 0 ; i < n ; i++){
    if(isCanSit(i)){
      chair[i] = 'A';
      isZero = false;
      return;
    }
  }
}

bool isNext(int x){
  if(chair[x-1] == 'A' || chair[x+1] == 'A') return true;
  return false;
}

void B(){
  for(int i = n-1 ; i >= 0 ; i--){
    if(isCanSit(i) && !isNext(i)){
      chair[i] = 'B';
      isZero = false;
      return;
    }
  }
  
  for(int i = 0 ; i < n ; i++){
    if(isCanSit(i)){
      chair[i] = 'B';
      isZero = false;
      return;
    }
  }
}

void C(){
  if(isZero){
    if(n % 2 == 1) chair[n/2] = 'C';
    else chair[n/2] = 'C';
    isZero = false;
    return;
  }
  
  for(int i = 0 ; i < n ; i++){
    if(!isCanSit(i)){
      if(isCanSit(i+1)){
	chair[i+1] = 'C';
	isZero = false;
	return;
      }
      else if(isCanSit(i-1)){
	chair[i-1] = 'C';
	isZero = false;
	return;
      }
    }
  }
}

bool DcanSitNoneNext(int x){
  if(x == n-1){
    if(chair[x-1] == '#') return true;
  }
  if(x == 0){
    if(chair[x+1] == '#') return true;
 }  
  if(chair[x-1] == '#' && chair[x+1] == '#') return true;
  return false;
}

int calcDisD(int x){
  int ret, cnt = 0;
  for(int i = x-1 ; i >= 0 ; i--){ // left
    if(chair[i] != '#') break;
    else cnt++;
  }
  
  ret = cnt;
  cnt = 0;
  
  for(int i = x+1 ; i < n ; i++){ // right
    if(chair[i] != '#') break;
    else cnt++;
  }
  
  ret = max(ret, cnt);
  return ret;
}

void D(){
  if(isZero){
    chair[0] = 'D';
    isZero = false;
    return;
  }
  
  int sit;
  int dis[MAX];
  fill(dis, dis+MAX, MAX);
  for(int i = 0 ; i < n ; i++){
    if(chair[i] != '#'){
      for(int j = 0 ; j < n ; j++){
	dis[j] = min(dis[j], abs(i-j));
      }
    }
  }  
  int d = 0;
  for(int i = 0 ; i < n ; i++){
    if(dis[i] > d){
      sit = i;
      d = dis[i];
    }
  }
  chair[sit] = 'D';
  return;
}
  
void init(){
  fill(chair, chair+MAX, '#');
  isZero = true;
}

void display(){
  for(int i = 0 ; i < n ; i++){
    cout << chair[i];
  }
  cout << endl;
}

int main(){
  char p;
  while(cin >> n >> m){
    if(n == 0 && m == 0) break;
    init();
    for(int i = 0 ; i < m ; i++){
      cin >> p;
      if(p == 'A') A();
      if(p == 'B') B();
      if(p == 'C') C();
      if(p == 'D') D();
      display();
    }
    display();
  }
  return 0;
}

C++: #include<iostream>
using namespace std;
#define REP(i,b,n) for(int i=b;i<n;i++)
#define rep(i,n)   REP(i,0,n)

int findlm(int n,char *in){
  rep(i,n)if(in[i] == 0)return i;
}

int findNotA(int n,char *in){
  for(int i=n-1;i>=0;i--){
    if (in[i] == 0 && (i==0||in[i-1]!= 'A') && (i == n-1 || in[i+1] != 'A'))return i;
  }
  return -1;
}

int nextP(int n,char *in){
  rep(i,n){
    if (in[i] != 0){
      if (i < n-1 && in[i+1] == 0)return i+1;
      if (i >0 && in[i-1] == 0)return i-1;
    }
  }
  return -1;
}

int notNextP(int n,char *in){
  int ret = -1,maxdist=0;
  rep(i,n){
    if( in[i] != 0)continue;
    int tmpdist = 0;
    for(int j=i-1;j>=0;j--){
      if (in[j] != 0){tmpdist=i-j;break;}
    }
    for(int j=i+1;j<n;j++){
      if (in[j] != 0){tmpdist=max(tmpdist,j-i);break;}
    }
    if (tmpdist > maxdist)ret=i,maxdist = tmpdist;
  }
  return ret;
}

void put(int n,char *in,char inp){
  int index = -1;
  if (inp == 'A'){
    index = findlm(n,in);
  }else if (inp == 'B'){
    index = findNotA(n,in);
    if (index == -1)index = findlm(n,in);
  }else if (inp == 'C'){
    index = nextP(n,in);
    if (index == -1)index = n%2 == 0?(n)/2:n/2;
  }else if (inp == 'D'){
    index = notNextP(n,in);
    if (index == -1)index = 0;
  }
  in[index] = inp;
}


main(){
  char op[255];
  op['A']='A';  op['B']='B';  op['C']='C';  op['D']='D';
  op[0]='#';

  int n,m;
  char in[100];
  while(cin>>n>>m && n){
    rep(i,n)in[i] = 0;
    rep(i,m){
      char inp;
      cin>>inp;
      put(n,in,inp);
    }
    rep(i,n)cout << op[in[i]] ;
    cout << endl;
  }


}

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;
}