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<stdio.h>
#include<string.h>
#include<math.h>
int main(void)
{
	int a,s,d[100],f,g,h,i,j,k,c,x[3],o;
	char z[2];
	while(1){
		scanf("%d %d",&a,&s);
		if(a==0&&s==0) break;
		f=a;
		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;
						f--;
						break;
					}
				}
			}
			else if(z[0]=='B'){
				g=0;
				for(j=a-1;j>=0;j--){
					if(d[j]==0&&d[j+1]!=1&&d[j-1]!=1){
						d[j]=2;
						f--;
						break;
					}
					if(d[j]==0) g++;
					if(f==g){
						d[j]=2;
						f--;
						break;
					}
				}
			}
			else if(z[0]=='C'){
				if(a==f){
					if(a%2==1){
						d[((a+1)/2)-1]=3;
						f--;
					}
					else if(a%2==0){
						d[a/2]=3;
						f--;
					}
				}
				else if(a>f){
					for(j=0;j<a;j++){
						if(d[j]>0){
							if(d[j+1]==0&&j+1<a){
								d[j+1]=3;
								f--;
								break;
							}
							else if(d[j-1]==0&&j-1>=0){
								d[j-1]=3;
								f--;
								break;
							}
						}
					}
				}
			}
			else if(z[0]=='D'){
				h=-1;
				c=-1;
				int v=0;
				x[0]=0;
				x[1]=0;
				for(j=a-1;j>=0;j--){
					if(d[j]>0&&v==0){
						h=j;
						if(d[0]==0){
							x[0]=h-1;
							x[1]=0;
						}
						v=1;
					}
					else if(d[j]>0&&v==1){
						c=j;
					}
					if(c>-1&&h>-1){
						if((h-c)%2==1){
							if(x[0]<=((h-c)/2-1)){
								x[0]=(h-c)/2-1;
								x[1]=h-(h-c)/2-1;
							}
						}
						else if((h-c)%2==0){
							if(x[0]<=(h-c)/2){
								x[0]=(h-c)/2;
								x[1]=h-(h-c)/2;
							}
						}
					}
					if(c>-1) h=c;
				}
				if(d[a-1]==0){
					if(x[0]<(a-1)-c){
						x[0]=(a-1)-c;
						x[1]=a-1;
					}
				}
				if(h==-1) x[1]=0;
				else if(c==-1){
					x[0]=(a-1)-h;
					x[1]=a-1;
					if(x[0]<h) x[1]=0;
				}
				d[x[1]]=4;
				f--;
			}
		}
		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 <iostream>
#include <string>
#include <algorithm>
using namespace std;

int main()
{
  int n, m;
  while (cin >> n >> m) {
    string chair(n, '#');

    while (m--) {
      string a;
      cin >> a;
      if (a == "A") {
	for (int i = 0; i < n; ++i) {
	  if (chair[i] == '#') {
	    chair[i] = 'A';
	    break;
	  }
	}
      } else if (a == "B") {
	bool sit = false;
	for (int i = n-1; i > 0; --i) {
	  if (i == 0 && chair[i+1] != 'A') {
	    chair[i] = 'B';
	    sit = true;
	    break;
	  } else if (i == n-1 && chair[i] == '#' && chair[i-1] != 'A') {
	    chair[i] = 'B';
	    sit = true;
	    break;
	  } else if (chair[i] == '#' &&  chair[i+1] != 'A' && chair[i-1] != 'A') {
	    chair[i] = 'B';
	    sit = true;
	    break;
	  }
	}
	if (sit)
	  continue;

	for (int i = 0; i < n; ++i) {
	  if (chair[i] == '#') {
	    chair[i] = 'B';
	    break;
	  }
	}
      } else if (a  == "C") {
	bool sit = false;
	for (int i = 0; i < n; ++i) {
	  if (i == 0 && chair[i] != '#' && chair[i+1] == '#') {
	    chair[i+1] = 'C';
	    sit = true;
	    break;
	  } else if (i == n-1 && chair[i] != '#' && chair[i-1] == '#') {
	    chair[i+1] = 'C';
	    sit = true;
	    break;
	  } else if (chair[i] != '#') {
	    if (chair[i+1] == '#') {
	      chair[i+1] = 'C';
	      sit = true;
	      break;
	    } else if (chair[i-1] == '#') {
	      chair[i+1] = 'C';
	      sit = true;
	      break;
	    }
	  }
	}
	if (sit)
	  continue;

	if (n&1)
	  chair[(n+1)/2-1] = 'C';
	else
	  chair[n/2] = 'C';
      } else {
	int maxIndex = -1, dist = -1;
	for (int i = 0; i < n; ++i) {
	  if (chair[i] != '#')
	    continue;

	  int right = 0;
	  if (i == n-1)
	    right = n;
	  for (int j = i+1; j < n; ++j) {
	    if (chair[j] == '#')
	      ++right;
	    else
	      break;
	  }

	  int left = 0;
	  if (i == 0)
	    left = n;
	  for (int j = i-1; j >= 0; --j) {
	    if (chair[j] == '#')
	      ++left;
	    else
	      break;
	  }

	  if (dist < min(right, left)) {
	    maxIndex = i;
	    dist = min(right, left);
	  }
	}
	chair[maxIndex] = 'D';
      }
    }

    cout << chair << 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;
			}
		}
	}
	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;
}