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[:len(chair)-1], ""))
	}
}

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 <algorithm>
#include <vector>
#include <string>
#include <numeric>
#include <stdio.h>

using namespace std;

const int inf = 1e9 + 7;

int main() {

	while (1) {
		int n, m;
		cin >> n >> m;
		if (n == 0 && m == 0) break;
		vector<char> a(m);
		for (int i = 0; i < m; i++) cin >> a[i];

		vector<int> dis(n, inf);
		// 順にやってけばいいのかな
		vector<char> ans(n, '#');
		for (int i = 0; i < m; i++) {
			if (a[i] == 'A') {
				// 左から座る
				for (int j = 0; j < n; j++) {
					if (ans[j] == '#') {
						ans[j] = a[i];
						break;
					}
				}
			}
			else if (a[i] == 'B') {
				// 右から座る
				bool ok = false;
				for (int j = n - 1; j >= 0; j--) {
					if (ans[j] == '#') {
						// 隣がA国人か
						if (j + 1 < n) if (ans[j + 1] == 'A')continue;
						if (j - 1 >= 0) if (ans[j - 1] == 'A') continue;
						ans[j] = a[i];
						ok = true;
						break;
					}
				}
				if (!ok) { // まだ座れてなかったら
					for (int j = 0; j < n; j++) {
						if (ans[j] == '#') {
							ans[j] = a[i];
							break;
						}
					}
				}
			}
			else if (a[i] == 'C') {
				if (i == 0) {
					// 始めの人
					if (n % 2 == 1) ans[(n + 1) / 2 - 1] = a[i];
					else ans[n / 2] = a[i];
					continue;
				}
					// 左から人がいるかみてく
				for (int j = 0; j < n; j++) {
					if (ans[j] != '#') {
						bool ok = false;
						if (j + 1 < n) {
							if (ans[j + 1] == '#') {
								ans[j + 1] = a[i];
								ok = true;
								break;
							}
						}
						if (j - 1 >= 0) {
							if (ans[j - 1] == '#') {
								ans[j - 1] = a[i];
								ok = true;
								break;
							}
						}
						if (!ok) continue;
					}
				}
			}
			else if (a[i] == 'D') {
				if (i == 0) {
					ans[0] = a[i];
					continue;
				}
				// 一番近い人との距離をそれぞれ求める
				// 左右両方から調べる
				int cnt = inf - n;
				for (int j = 0; j < n; j++) {
					if (ans[j] != '#') {
						dis[j] = 0;
						cnt = 0;
					}
					else {
						dis[j] = ++cnt;
					}
				}
				// 反対からも
				for (int j = n - 1; j >= 0; j--) {
					if (ans[j] != '#') {
						cnt = 0;
					}
					else {
						dis[j] = min(++cnt, dis[j]);
					}
				}

				// 一番遠いい点を探す
				int jmax = -1;
				int dismax = -1;
				for (int j = 0; j < n; j++) {
					if (dismax < dis[j]) {
						jmax = j;
						dismax = dis[j];
					}
				}

				ans[jmax] = a[i];
			}
		}

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

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int n,m;
char t[120];

void A(char a){
  int i=1;
  while(t[i]!=0) i++;
  t[i]=a;
}

void B(){
  for(int i=n;i>=1;i--){
    if(t[i]==0){
      t[i]='B';
      break;
    }
  }
}

void C(int cnt){
  if(cnt==0) {
    if(n%2==0) t[n/2+1]='C';
    else t[(n+1)/2]='C';
    return;
  }


  for(int i=1;i<=n;i++){
    if(t[i]!=0&&t[i+1]==0) {
      t[i+1]='C';
      break;
    }
    if(t[i]!=0&&t[i-1]==0){
      t[i-1]='C';
      break;
    }
  }
}

void D(int cnt){
  if(cnt==0){
    t[1]='D';
    return;
  }
  int mx=0,idx=0,c=0;
  for(int i=1;i<=n;i++) {
    if(t[i]==0) c++;
    else c=0;
    if(mx+mx%2<c)mx=c,idx=i;
  }

  if(mx<=2&&c==2&&mx<c) {
    t[n]='D';
    return;
  }  

  if(mx<=2){
    A('D');
    return ;
  }

  if(idx==n) t[n]='D';
  else   t[(idx-(idx-mx+1))/2+(idx-mx+1)]='D';
}

int main(){
  while(1){
    cin>>n>>m;
    if(!n&&!m)break;
    memset(t,0,sizeof(t));
    t[0]=t[n+1]=1;
    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(i);
    }

    for(int i=1;i<=n;i++)if(t[i]==0)t[i]='#';
    t[n+1]=0;
    printf("%s\n",t+1);
  }
  return 0;
}

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

#define REP(i,n,m) for(int i=n;i<m;i++)
#define rep(i,n) REP(i,0,n)

int n;
char s[104];

int A(void){
	rep(i,n) if(s[i] == '#') return i;
	return -1;
}

int B(void){
	for(int i=n-1;i>=0;i--){
		if(s[i] == '#'){
			int l = i - 1;
			int r = i + 1;
			if(l >= 0 && s[l] == 'A') continue;
			if(r < n && s[r] == 'A') continue;

			return i;
		}
	}

	return -1;
}

int C(void){
	rep(i,n){
		if(s[i] != '#'){
			int l = i - 1;
			int r = i + 1;
			if(l >= 0 && s[l] == '#') return l;
			if(r < n && s[r] == '#') return r;
		}
	}

	return -1;
}

int D(void){
	int res = -1;
	int maxDist = 0;

	rep(i,n){
		if(s[i] == '#'){
			int ldist;
			int rdist;

			for(ldist=i-1;ldist>=0 && s[ldist]=='#';ldist--);
			for(rdist=i+1;rdist<n && s[rdist]=='#';rdist++);

			ldist = i - ldist;
			rdist = rdist - i;

			if(maxDist < min(ldist,rdist)){
				res = i;
				maxDist = min(ldist,rdist);
			}
		}
	}

	return res;
}

int main(void){
	int m;

	while(cin>>n>>m && (n||m)){
		memset(s,'#',sizeof(s));

		rep(i,m){
			int idx;
			char ch;
			cin>>ch;

			switch(ch){
			case 'A':
				s[A()] = 'A';
				break;
			case 'B':
				idx = B();
				s[(idx == -1 ? A() : idx)] = 'B';
				break;
			case 'C':
				idx = C();
				s[(idx == -1 ? n%2==0 ? n/2 : n/2 : idx)] = 'C';
				break;
			case 'D':
				s[(i == 0 ? 0 : D())] = 'D';
				break;
			}
		}

		rep(i,n) cout<<s[i];
		cout<<endl;
	}

	return 0;
}