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] = 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<bits/stdc++.h>
using namespace std;
int main(){
  int n,m;
  while(cin>>n>>m,n){
    string s;
    for(int i=0;i<n;i++)s+='#';
    while(m--){
      string p;
      cin>>p;
      if(p=="A"){
        for(int i=0;i<n;i++)
          if(s[i]=='#'){
            s[i]='A';
            break;
          }
      }
      if(p=="B"){
        int pp=0;
        for(int i=n-1;i>=0;i--){
          if(i==n-1){if(s[i-1]!='A'&&s[i]=='#'){pp++,s[i]='B';break;}}
          else if(!i){if(s[i+1]!='A'&&s[i]=='#'){pp++,s[i]='B';break;}}
          else {if(s[i-1]!='A'&&s[i]=='#'&&s[i+1]!='A'){pp++,s[i]='B';break;}}
        }
        if(!pp)for(int i=0;i<n;i++)
             if(s[i]=='#'){
               s[i]='B';
               break;
            }
      }
      if(p=="C"){
        int pp=0;
        for(int i=0;i<n;i++)
          if(s[i]!='#'){
            
            if(i!=n-1){if(s[i+1]=='#'){s[i+1]='C';pp++;break;}}
            if(i){if(s[i-1]=='#'){s[i-1]='C';pp++;break;}}
          }
        if(!pp){
          if(n%2)s[(n+1)/2-1]='C';
          else s[n/2]='C';
        }
      }
      else if(p=="D"){
        int d[n]={},p=0,sp=0;
        for(int i=0;i<n;i++){

          int p1=0,p2=0;
          if(i==n-1)p1=100;
          for(int j=i;j<n;j++)
            if(s[j]=='#')p1++;
            else break;
          for(int j=i;j>=0;j--)
            if(s[j]=='#')p2++;
            else break;
          p1=min(p1,p2);
          p=max(p,p1);
          d[i]=p1;
        }
        for(int i=0;i<n;i++)if(s[i]!='#')sp++;
        if(sp)s[0]='D';
        else for(int i=0;i<n;i++)
          if(d[i]==p){
            s[i]='D';
            break;
          }
      }

    }
    cout<<s<<endl;
  }
}

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

char map[101];
int n,m;

void sheet(string hit){
	int a=0;
	bool ch=false;
	if(hit[0]=='A'){
		while(1){
			if(map[a]=='#'){
				map[a]='A';
				break;
			}
			a++;
		}
	}
	if(hit[0]=='B'){
		for(a=n-1;a>=0;a--){
			if(map[a]=='#' && map[a-1]!='A' && map[a+1]!='A'){
				map[a]='B';
				ch=true;
				break;
			}
		}
		if(!ch){
			while(1){
				if(map[a]=='#'){
					map[a]='B';
					break;
				}
				a++;
			}
		}
	}
	if(hit[0]=='C'){
		for(a=0;a<n;a++){
			if(map[a]=='#' &&((map[a-1]!='#' && a>0)||(map[a+1]!='#' && a<n-1))){
				map[a]='C';
				ch=true;
				break;
			}
		}
		if(!ch){
			if(n%2==0)map[n/2]='C';
			if(n%2==1)map[(n+1)/2-1]='C';
		}
	}
	if(hit[0]=='D'){
		int maxIndex = -1, dist = -1;
		for (int i = 0; i < n; ++i) {
			if(map[i] != '#')continue;
			int right = 0;
			if(i == n-1)right = n;
			for(int j = i+1; j < n; ++j) {
				if (map[j] == '#')++right;
				else break;
			}
			int left = 0;
			if (i == 0)left = n;
			for (int j = i-1; j >= 0; --j) {
				if (map[j] == '#')++left;
				else break;
			}
			if (dist < min(right, left)) {
				maxIndex = i;
			    dist = min(right, left);
			}
		}
		map[maxIndex] = 'D';
    }
}

int main(void){
	int a;
	while(1){
		for(a=0;a<=100;a++){
			map[a]='#';
		}
		cin >> n >> m;
		if(n==0 && m==0)break;
		for(a=0;a<m;a++){
			string hito;
			cin >> hito;
			sheet(hito);
		}
		for(a=0;a<n;a++)cout << map[a];
		cout << endl;
	}
	return 0;
}