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>
using namespace std;
int m,n,j,k,f,g;
char c[101];
void acta() {
	for (j=0;j<m;j++) if (c[j]=='#') { c[j]='A'; break;}
}

void actb() {
	f=m-1;
	for (j=m-1;j>=0;j--) {
		if (c[j]!='#') continue;
		f=j;
		if (j==m-1) {if (c[m-2]!='A') break; else continue;} 
		if (j==0) {if (c[1]!='A') break; else continue;}
		if (c[j-1]!='A' && c[j+1]!='A') break;
	}
	c[f]='B';
}

void actc() {
	if (g==0) {c[(m-1)/2]='C'; return;}
	for (j=0;j<m;j++) {
	 if (c[j]!='#') {
		 if (j<m-1) if (c[j+1]=='#') { c[j+1]='C'; break;}
		 if (j>0) if (c[j-1]=='#') { c[j-1]='C'; break;}
	 }   	
	}
}
void actd() {
	int l=0,sx=0,x=0;
	f=0;
	if (g==0) {c[0]='D';return;}
	for (j=0;j<m;j++) {
		if (c[j]!='#') {
			if (f==0) { x=0; l=j;} else { if ((j-sx)/2>l) { l=(j-sx)/2; x=sx+l;}}
			sx=j; f=1;
		} else if (j==m-1) if (j-sx>l) x=j;
	}
	c[x]='D';
}
int main() {
	int i;
	char a;
	while(cin >> m >> n) {
		if (m+n==0) break;
		for (i=0;i<m;i++) c[i]='#'; c[i]='\0'; g=0;
		for (i=0;i<n;i++) {
			cin >> a;
			switch(a) {
				case 'A': acta(); break;
				case 'B': actb(); break;
				case 'C': actc(); break;
				case 'D': actd(); break;
			}
			g=1;
		}
		cout << c << endl;
	}	 
			  			
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <set>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,j) FOR(i,0,j)
#define mp std::make_pair

typedef long long ll;
typedef unsigned long long ull;
typedef std::pair<int,int> P;
typedef std::pair<int,P> State;

const int INF = 1001001001;

// S N E W(南北東西)
const int dx[8] = {0, 0, 1, -1, 1, 1, -1, -1}, dy[8] = {1, -1, 0, 0, 1, -1, 1, -1};

int N, M;
char chairs[100];

int main(){
    while(std::cin >> N >> M, N){
        REP(i, N){chairs[i] = '#';}

        REP(i, M){
            char c;
            std::cin >> c;

            if(c == 'A'){
                REP(j, N){
                    if(chairs[j] == '#'){chairs[j] = 'A'; break;}
                }
            }else if(c == 'B'){
                bool can = false;
                for(int j=N-1;j>=0;j--){
                    if(chairs[j] != '#'){continue;}
                    if(j-1 >= 0 && chairs[j-1] == 'A'){continue;}
                    if(j+1 < N && chairs[j+1] == 'A'){continue;}
                    chairs[j] = 'B';
                    can = true;
                    break;
                }
                if(can){continue;}
                REP(j, N){
                    if(chairs[j] == '#'){chairs[j] = 'B'; break;}
                }
            }else if(c == 'C'){
                if(i == 0){chairs[N/2] = 'C'; continue;}

                REP(j, N){
                    if(chairs[j] == '#'){continue;}
                    if(j+1 < N && chairs[j+1] == '#'){chairs[j+1] = 'C'; break;}
                    if(j-1 >= 0 && chairs[j-1] == '#'){chairs[j-1] = 'C'; break;}
                }
            }else if(c == 'D'){
                int pos = -1, max_l = 0;
                REP(j, N){
                    if(chairs[j] != '#'){continue;}

                    int l1 = INF, l2 = INF;
                    for(int k=j-1;k>=0;k--){
                        if(chairs[k] != '#'){l1 = j-k; break;}
                    }
                    for(int k=j+1;k<N;k++){
                        if(chairs[k] != '#'){l2 = k-j; break;}
                    }

                    if(std::min(l1, l2) > max_l){pos = j; max_l = std::min(l1, l2);}
                }

                chairs[pos] = 'D';
            }
        }

        REP(i, N){
            putchar(chairs[i]);
        }
        puts("");
    }
}