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 <vector>
#include <string.h>
using namespace std;

void sit_seat(char c, vector<char>& seat)
{
	if(c == 'A')
	{
		for(int i=0; i<seat.size(); i++)
		{
			if(seat[i] == 0)
			{
				seat[i] = c;
				break;
			}
		}
	}
	else if(c == 'B')
	{
		bool is_sit = false;
		for(int i=seat.size()-1; i>=0; i--)
		{
			if(seat[i] != 0) continue;

			int r = i+1;
			if(r>=0 && r<seat.size())
			{
				if(seat[r] == 'A') continue;
			}

			int l = i-1;
			if(l>=0 && l<seat.size())
			{
				if(seat[l] == 'A') continue;
			}

			seat[i] = c;
			is_sit = true;
			break;
		}

		if(!is_sit)
		{
			for(int i=0; i<seat.size(); i++)
			{
				if(seat[i] == 0) seat[i] = c;
			}
		}
	}
	else if(c == 'C')
	{
		bool is_sit = false;
		for(int i=0; i<seat.size(); i++)
		{
			if(seat[i] != 0) continue;
			int r = i+1;
			if(r>=0 && r<seat.size())
			{
				if(seat[r] != 0)
				{
					seat[i] = c;
					is_sit = true;
					break;
				}
			}

			int l = i-1;
			if(l>=0 && l<seat.size())
			{
				if(seat[l] != 0)
				{
					seat[i] = c;
					is_sit = true;
					break;
				}
			}
		}

		if(!is_sit)
		{
			if(seat.size() % 2 == 0)
			{
				seat[seat.size()/2+1] = c;
			}
			else
			{
				seat[(seat.size()+1)/2] = c;
			}
		}
	}
	else if(c == 'D')
	{
		bool is_people = false;
		for(int i=0; i<seat.size(); i++)
		{
			if(seat[i] != 0)
			{
				is_people = true;
				break;
			}
		}

		bool is_sit = false;
		if(!is_people)
		{
			seat[0] = c;
			is_sit = true;
		}

		if(!is_sit)
		{
			int mmd = 0;
			int p_sit = 0;
			for(int i=0; i<seat.size(); i++)
			{
				if(seat[i] != 0) continue;
				int r = i;
				while( 1 )
				{
					r++;
					if(r<0 || r>=seat.size())
					{
						r = 10000;
						break;
					}
					if(seat[r] != 0) break;
				}
				int rd = r - i;

				int l = i;
				while( 1 )
				{
					l--;
					if(l<0 || l>=seat.size())
					{
						l = -10000;
						break;
					}
					if(seat[l] != 0) break;
				}
				int ld = i - l;

				int d = min(rd, ld);
				if(mmd < d)
				{
					mmd = d;
					p_sit = i;
				}
			}
			
			seat[p_sit] = c;
		}
	}
	else
	{
		cout << "unknown nationality!" << endl;
		return;
	}
}

int main()
{
	int n, np;
	char c;
	while(cin >> n >> np, n|np)
	{
		vector<char> seat(n);
		memset(&seat[0], 0, sizeof(char)*n);

		for(int i=0; i<np; i++)
		{
			cin >> c;
			sit_seat(c, seat);
		}

		for(int i=0; i<n; i++)
		{
			if(seat[i] !=0) printf("%c", seat[i]);
			else printf("#");
		}
		printf("\n");
	}
}

C++: #include<iostream>
#define rep(i,n) for(int i=0;i<n;i++)
#define ck(a) (0<=a&&a<n)
using namespace std;
int main(){
	int n,m,s[100],f; char b[2];
	while(cin>>n>>m,n){
		rep(i,n)s[i]=0;
		rep(i,m){
			cin>>b;
			switch(b[0]){
			case 'A':
				rep(i,n)if(!s[i]){
					s[i]=1; break;
				}
				break;
			case 'B':
				f=1;
				rep(i,n)if(!s[n-1-i])
				if((!ck(n-2-i)||s[n-2-i]!=1)&&(!ck(n-i)||s[n-i]!=1)){
					s[n-1-i]=2,f=0; break;
				}
				if(f)rep(i,n)if(!s[n-1-i]){
					s[n-1-i]=2; break;
				}
				break;
			case 'C':
				f=1;
				rep(i,n)if(s[i]&&(ck(i+1)&&!s[i+1]||ck(i-1)&&!s[i-1])){
					if(ck(i+1)&&!s[i+1])s[i+1]=3;
					else s[i-1]=3;
					f=0; break;
				}
				if(f)s[n/2]=3;
				break;
			case 'D':
				int d,md=0,mdi=0;
				rep(i,n)if(!s[i]){
					for(d=1;i-d>=0||i+d<n;d++)if(ck(i+d)&&s[i+d]||ck(i-d)&&s[i-d])break;
					if(d>md)md=d,mdi=i;
				}
				s[mdi]=4;
				break;
			}
		}
		rep(i,n)cout<<char(s[i]?'A'-1+s[i]:'#'); cout<<endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <sstream>
#include <climits>
#include <cfloat>
#include <complex>

using namespace std;

int main()
{
	int n, m;
	while (scanf("%d %d", &n, &m), n | m)
	{
		char t[102];	// 1~n
		memset(t, '#', sizeof(t));
		for (int w = 0; w < m; ++w)
		{
			char c;
			scanf(" %c", &c);
			if (c == 'A')
			{
				int i;
				for (i = 1; t[i] != '#'; ++i)
					;
				t[i] = 'A';
			}
			else if (c == 'B')
			{
				int i;
				for (i = n; i >= 1; --i)
					if (t[i-1] != 'A' && t[i] == '#' && t[i+1] != 'A')
						break;
				if (i == 0)
					for (i = 1; t[i] != '#'; ++i)
						;
				t[i] = 'B';
			}
			else if (c == 'C')
			{
				int i;
				if (w == 0)
					i = n / 2 + 1;
				else
				{
					for (i = 1; t[i] == '#'; ++i)
						;
					++i;
				}
				t[i] = 'C';
			}
			else
			{
				int i;
				if (w == 0)
					i = 1;
				else
				{
					int dis[102];
					for (int j = 0; j < 102; ++j)
						dis[j] = 100000000;
					for (int j = 1; j <= n; ++j)
					{
						if (t[j] != '#')
							for (int k = 1; k <= n; ++k)
								dis[k] = min(dis[k], abs(j-k));
					}
					int d = 0;
					for (int j = 1; j <= n; ++j)
					{
						if (dis[j] > d)
						{
							i = j;
							d = dis[j];
						}
					}
				}
				t[i] = 'D';
			}
		}
		for (int i = 1; i <= n; ++i)
			putchar(t[i]);
		printf("\n");
	}

	return 0;
}