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>
using namespace std;
int n,m;
char t[100],ch;
void putA();
void putB();
void putC();
void putD();
int main(){
  while(cin>>n>>m){
    if(n==0&&m==0)break;
    for(int i=0;i<n;i++)t[i]='#';
    for(int i=0;i<m;i++){
      cin>>ch;
      if(ch=='A')putA();
      else if(ch=='B')putB();
      else if(ch=='C')putC();
      else putD();
    }
    for(int i=0;i<n;i++)cout<<t[i];
    cout<<endl;
  }
  return 0;
}
void putA(){
  for(int i=0;i<n;i++){
    if(t[i]!='#')continue;
    t[i]='A';
    return;
  }
}
void putB(){
  for(int i=n-1;i>=0;i--){
    if(t[i]!='#')continue;
    if(i-1>=0&&t[i-1]=='A')continue;
    if(i+1<n&&t[i+1]=='A')continue;
    t[i]='B';
    return;
  }
  for(int i=0;i<n;i++){
    if(t[i]=='#'){
      t[i]='B';
      return;
    }
  }
}
void putC(){
  for(int i=0;i<n;i++){
    if(t[i]=='#')continue;
    if(i+1<n&&t[i+1]=='#'){
      t[i+1]='C';return;
    }else if(i-1>=0&&t[i-1]=='#'){
      t[i-1]='C';return;
    }
  }
  t[n/2]='C';
}
void putD(){
  bool flg=true;
  for(int i=0;i<n;i++)if(t[i]!='#')flg=false;
  if(flg){
    t[0]='D';return;
  }

  int l[100],r[100],m[100];
  l[0]=999;
  for(int i=1;i<n;i++){
    if(t[i]=='#')l[i]=l[i-1]+1;
    else l[i]=0;
  }
  r[n-1]=999;
  for(int i=n-2;i>=0;i--){
    if(t[i]=='#')r[i]=r[i+1]+1;
    else r[i]=0;
  }
  for(int i=0;i<n;i++){
    m[i]=min(l[i],r[i]);
  }
  int pos=-1,mini=100;
  for(int i=0;i<n;i++){
    if(t[i]!='#')continue;
    if(m[i]<mini){
      pos=i;
      mini=m[i];
    }
  }
  if(pos!=-1){
    t[pos]='D';
  }
}

C++: #include <string>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
void solve1(string& s, char c) {
	s[s.find('#')] = c;
}
void solve2(string& s) {
	for (int i = s.size() - 1; i >= 0; i--) {
		if (!((i < s.size() - 1 && s[i + 1] == 'A') || (i > 0 && s[i - 1] == 'A'))) {
			s[i] = 'B'; return;
		}
	}
	solve1(s, 'B');
}
vector<int> dist(string& s) {
	vector<int> ret(s.size(), 999999999);
	for (int i = 0; i < s.size(); i++) {
		if (s[i] != '#') {
			for (int j = 0; j < s.size(); j++) {
				ret[j] = min(ret[j], abs(i - j));
			}
		}
	}
	return ret;
}
void solve3(string &s) {
	for (int i = 0; i < s.size(); i++) {
		if (s[i] != '#') {
			if (i < s.size() - 1 && s[i + 1] == '#') {
				s[i + 1] = 'C'; return;
			}
			if (i > 0 && s[i - 1] == '#') {
				s[i - 1] = 'C'; return;
			}
		}
	}
	if (s.size() % 2 == 1) s[(s.size() - 1) / 2] = 'C';
	else s[s.size() / 2] = 'C';
}
void solve4(string &s) {
	vector<int> ret = dist(s);
	s[max_element(ret.begin(), ret.end()) - ret.begin()] = 'D';
}
int N, Q;
int main() {
	while (cin >> N >> Q, N) {
		string s(N, '#'), t;
		while (Q--) {
			cin >> t;
			if (t == "A") solve1(s, 'A');
			if (t == "B") solve2(s);
			if (t == "C") solve3(s);
			if (t == "D") solve4(s);
		}
		cout << s << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <string>
using namespace std;
#define MAX 100
int main(){
	int seat,people;
	while(cin>>seat>>people){
		if(seat+people==0 )break;
		string str[101],x;
		for( int i=0 ; i<=MAX ; i++ )
			str[i]="#";
		for( int i=0 ; i<people ; i++ ){
			cin>>x;
			if(x=="A"){
				for( int j=0 ; j<seat ; j++ ){
					if(str[j]=="#"){
						str[j]="A";
						break;
					}
				}
			}

			else if(x=="B"){
				int all_b_sign=0;
				for(int j=seat-1 ; j>=0 ; j-- ){
					if(str[j]=="#"){
						int B_sign=0;
						if(j==0)
							B_sign=1;
						else if(j==seat-1)
							if(str[j-1]!="A")
								B_sign=1;
						else if(str[j+1]!="A"&&str[j-1]!="A")
							B_sign=1;
						if(B_sign==1){
							str[j]="B";
							all_b_sign=1;
							break;
						}
					}
				}
				if(all_b_sign==0){
					for(int j=0 ; j<seat ; j++ ){
						if(str[j]=="#"){
							str[j]="B";
							break;
						}
					}
				}
			}

			else if(x=="C"){
				int c_sign=0;
				for(int j=0 ; j<seat ; j++ ){
					if(str[j]!="#"){
						if(j==seat-1){
							if(str[j-1]=="#"){
								str[j-1]="C";
								c_sign=1;
								break;
							}
						}
						else if(j==0){
							if(str[j+1]=="#"){
								str[j+1]="C";
								c_sign=1;
								break;
							}
						}
						else if(str[j+1]=="#"){
							str[j+1]="C";
							c_sign=1;
							break;
						}
						else if(str[j-1]=="#"){
							str[j-1]="C";
							c_sign=1;
							break;
						}

					}
				}
				if(c_sign==0){
					if(seat%2)
						str[(seat+1)/2]="C";
					else
						str[seat/(2+1)]="C";
				}
			}

			else if(x=="D"){
				if(i==0){
					str[0]="D";
					continue;
				}
				int location,max=0;
				for( int j=seat-1 ; j>=0 ; j-- ){
					int l=j;
					while(l>0){
						if(str[l]!="#"){
							if(max<=j-l){
								max=j-l;
								location=j;
							}
							break;
						}
						l--;
					}
					l=j;
					while(l<seat){
						if(str[l]!="#"){
							if(max<=l-j){
								max=l-j;
								location=j;
							}
							break;
						}
						l++;
					}
				}
				str[location]="D";
			}

		}
		for(int i=0 ; i<seat ; i++ )
			cout<<str[i];
		cout<<endl;
	}
}