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<algorithm>
#include<cstdio>
using namespace std;
#define INF (1 << 29)
int main(){
  char chair[105];
  int n, m;
  char c;
  while(cin >> n >> m, n){
    fill(chair, chair + n, '#');
    chair[n] = 0;
    for(int i = 0;i < m;i++){
      cin >> c;
      switch(c){
      case 'A':
      left :
	for(int j = 0;j < n;j++){
	  if(chair[j] == '#'){
	    chair[j] = c;
	    break;
	  }
	}
	break;
      case 'B':
	for(int j = n - 1;j >= 0;j--){
	  if((j == 0 || chair[j - 1] != 'A') && chair[j + 1] != 'A' && chair[j] == '#'){
	    chair[j] = c;
	    break;
	  }
	  if(j == 0)goto left;
	}
	break;
      case 'C':
	for(int j = 0;j < n;j++){
	  if(j != '#'){
	    if(chair[j + 1] == '#'){
	      chair[j + 1] = c;
	      break;
	    }
	    if(j != 0 && chair[j - 1] == '#'){
	      chair[j - 1] = c;
	      break;
	    }
	  }
	  if(j == n - 1){
	    chair[n / 2] = c;
	  }
	}
	break;
      case 'D':
	int p = 0, s = -1;
	for(int j = 0;j < n;j++){
	  if(chair[j] != '#')continue;
	  int t = INF;
	  for(int k = j;k < n;k++){
	    if(chair[k] != '#'){
	      t = k - j;
	    }
	  }
	  for(int k = j;k >= 0;k--){
	    if(chair[k] != '#'){
	      t = min(t, j - k);
	    }
	  }
	  if(t > s){
	    p = j;
	    s = t;
	  }
	}
	if(p == INF){
	  chair[n - 1] = c;
	}
	else{
	  chair[p] = c;
	}
	break;
      }
    }
    printf("%s\n", chair);
  }
  return 0;
}

C++: #define _USE_MATH_DEFINES
#include<cstdio>
#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#include<stack>
#include<cmath>
#include<climits>
using namespace std;

int N, M;
char C;
char chairs[102];

void PutA(){
	for(int i = 1; i <= N; i++){
		if(chairs[i] == '#'){
			chairs[i] = 'A';
			return;
		}
	}
}

void PutB(){
	for(int i = N; i >= 1; i--){
		if(chairs[i+1] != 'A' && chairs[i] == '#' && chairs[i-1] != 'A'){
			chairs[i] = 'B';
			return;
		}
	}
	for(int i = 1; i <= N; i++){
		if(chairs[i] == '#'){
			chairs[i] = 'B';
			return;
		}
	}
}

void PutC(){
	for(int i = 1; i <= N; i++){
		if(chairs[i] != '#'){
			if(chairs[i+1] == '#'){
				chairs[i+1] = 'C';
				return;
			}
			if(chairs[i-1] == '#'){
				chairs[i-1] = 'C';
				return;
			}
		}
	}
	if(N&1) chairs[ (N+1)/2 ] = 'C';
	chairs[N/2 + 1] = 'C';
}

void PutD(){
	int l[102], r[102];
	l[0] = INT_MAX/2; r[N+1] = INT_MAX/2;
	for(int i = 1; i <= N; i++) l[i] = (chairs[i] == '#') ? l[i-1] + 1 : 0;
	for(int i = N; i >= 1; i--) r[i] = (chairs[i] == '#') ? r[i+1] + 1 : 0;

	int ma_idx, ma_d = -1;
	for(int i = 1; i <= N; i++){
		int d = min(l[i], r[i]);
		if(d >= INT_MAX/2) d = INT_MAX;
		if(ma_d < d){
			ma_idx = i; ma_d = d;
		}
	}
	chairs[ma_idx] = 'D';
}

int main(){
	void (*put[4])() = {PutA, PutB, PutC, PutD};

	while(cin >> N >> M, N || M){
		fill_n(chairs, N+2, '#');
		chairs[0] = chairs[N+1] = '.';
		for(int i = 0; i < M; i++){
			cin >> C;
			put[C - 'A']();
			for(int i = 1; i <= N; i++) printf("%c", chairs[i]); puts("");
		}
		for(int i = 1; i <= N; i++) printf("%c", chairs[i]); puts("");
	}
	return 0;
}

C++: #include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
const ld eps = 1e-9;

//// < "d:\d_download\visual studio 2015\projects\programing_contest_c++\debug\a.txt" > "d:\d_download\visual studio 2015\projects\programing_contest_c++\debug\b.txt"

void sit(vector<int>&seats, int who) {
	if (who == 1) {
		for (int i = 0; i < seats.size(); ++i) {
			if (!seats[i]) {
				seats[i] = who;
				return;
			}
		}
	}
	else if (who == 2) {
		for (int i = seats.size()-1; i >= 0; --i) {
			if (!seats[i]) {
				bool ok = true;
				for (int k = i+1; k >= i-1; k -= 2) {
					if (k >= 0 && k < seats.size()) {
						if (seats[k] == 1)ok = false;
					}
				}
				if (ok) {
					seats[i] = who;
					return;
				}
			}
		}
		for (int i = 0; i < seats.size(); ++i) {
			if (!seats[i]) {
				seats[i] = who;
				return;
			}
		}
	}
	else if (who == 3) {
		for (int i = 0; i < seats.size(); ++i) {
			if (seats[i]) {
				if (i!=seats.size()-1&&!seats[i+1]) {
					seats[i+1] = who;
					return;
				}
				else if (i != 0 && !seats[i - 1]) {
					seats[i - 1] = who;
					return;
				}
			}
		}
		seats[seats.size() / 2] = who;
		return;
	}
	else {
		vector<int>diss(seats.size(), 1000);
		for (int i = 0; i < seats.size(); ++i) {
			if (seats[i]) {
				diss[i] = 0;
				for (int j = i - 1; j >= 0; --j) {
					diss[j] = min(diss[j], i-j);
				}
				for (int j = i + 1; j < seats.size(); ++j) {
					diss[j] = min(diss[j], j - i);
				}
			}
		}
		int maxdis = -1;
		int ans = -1;
		for (int i = 0; i < seats.size(); ++i) {
			if (maxdis < diss[i]) {
				maxdis = diss[i];
				ans = i;
			}
		}
		seats[ans] = who;
		return;
	}
	assert(false);
}

int main() {
	while (1) {
		int N, M; cin >> N >> M;
		if (!N)break;
		vector<int>seats(N);
		for (int i = 0; i < M; ++i) {
			char c; cin >> c;
			int num = c - 'A' + 1;
			sit(seats, num); 
			
		}
		for (int i = 0; i < N; ++i) {
			if (seats[i]) {
				cout << char('A' + seats[i] - 1);
			}
			else {
				cout << '#';
			}
		}
		cout << endl;
	}
	return 0;
}