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<bits/stdc++.h>
using namespace std;
typedef long long int lld;

int main(){
  int n,m;
  while(cin >> n >> m , n){
    string str = "";
    for(int i=0;i<n;i++) str += '#';
    for(int c=0;c<m;c++){
      char h; cin >> h;
      if(h == 'A'){
	for(int i=0;i<n;i++){
	  if(str[i] == '#'){
	    str[i] = h;
	    break;
	  }
	}
      } else if(h == 'B'){
	int first = -1;
	bool flg = true;
	for(int i=n-1;i>=0;i--){
	  if(first == -1 && str[i] == '#') first = i;
	  if(i == n-1 && str[i] == '#' && str[i-1] != 'A'){
	    str[i] = h;
	    flg = false;
	    break;
	  } else if(i == 0 && str[i] == '#' && str[i+1] != 'A'){
	    str[i] = h;
	    flg = false;
	    break;
	  } else if(str[i] == '#' && str[i-1] != 'A' && str[i+1] != 'A'){
	    str[i] = h;
	    flg = false;
	    break;
	  }
	  if(flg) str[first] = h;
	}
      } else if(h == 'C'){
	if(c == 0) str[n/2] = h;
	else {
	  for(int i=0;i<n;i++){
	    if(str[i] != '#'){
	      if(str[i+1] == '#') {
		str[i+1] = h;
		break;
	      } else if(i-1 >= 0 && str[i-1] == '#') {
		str[i-1] = h;
		break;
	      }
	    }
	  }
	}
      } else {
	int first = -1;
	int idx = -1;
	int maxx = 0;
	for(int i=0;i<n;i++){
	  if(first == -1 && str[i] == '#') first = i;
	  if(str[i] != '#'){
	    int now = i;
	    int cnt = 0;
	    while(i+1 < n && str[i+1] == '#'){
	      if(first == -1 && str[i+1] == '#') first = i+1;
	      cnt++;
	      i++;
	    }
	    if(i+1 == n) {
	      if(cnt > maxx){
		maxx = cnt;
		idx = now + cnt;
	      }
	    }
	    else if(cnt > 2){
	      cnt = (cnt-1)/2;
	      if(cnt > maxx){
		maxx = cnt;
		idx = now + cnt + 1;
	      }
	    }
	  }
	}
	if(idx == -1) str[first] = h;
	else str[idx] = h;
      }
    }
    cout << str << endl;
  }
}

C++: #include <iostream>
#include <string>

using namespace std;

const int inf = 1e9;

int main(){
	int n, m;
	while(cin >> n >> m, n+m){
		string s;
		for(int i=0; i< n; i++) s+= "#";
		for(int i=0; i< m; i++){
			string t; cin >> t;
			if(t == "A"){
				for(int j=0; j< n; j++) if(s[j] == '#'){s[j] = 'A'; break;}
			}
			if(t == "B"){
				bool possible = false;
				for(int j=n-1; 0 <= j; j--){
					if(j == n-1 && s[j-1] != 'A'){s[j] = 'B'; possible = true; break;}
					else if(j == 0 && s[j+1] != 'A'){s[j] = 'B'; possible = true; break;}
					else if(s[j-1] != 'A' && s[j+1] != 'A'){s[j] = 'B'; possible = true; break;}
				}
				if(!possible){
					for(int j=0; j< n; j++){
						if(s[j] == '#'){s[j] = 'B'; break;}
					}
				}
			}
			if(t == "C"){
				bool possible = false;
				for(int j=0; j < n-1; j++){
					if(s[j] != '#' && s[j+1] == '#'){s[j+1] = 'C'; possible = true; break;}
				}
				if(!possible){
					for(int j= n-1; 1 <= j; j--){
						if(s[j] != '#' && s[j-1] == '#'){s[j-1] = 'C'; possible = true; break;}
					}
				}
				if(!possible){
					s[n/2] = 'C';
				}
			}
			if(t == "D"){
				int maxd = 0, p = 0;
				for(int j=0; j < n; j++){
					if(s[j] != '#') continue;
					int d = 0, idx = j;
					while(0 <= idx && s[idx] == '#') idx--;
					d = (idx == -1 ? inf : j-idx);
					idx = j;
					while(idx < n && s[idx] == '#') idx++;
					d = max(d, (idx == n ? inf : idx-j));
					if(maxd < d){maxd = d; p = j;}
				}
				s[p] = 'D';
			}
		}
		cout << s << endl;
	}
}

C++: #include <cstdio>
#include <string>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <iostream>

using namespace std;

int n,m;
int fie[101];
int dist[101];
char data[5]={'#','A','B','C','D',};

int main(void){
	while(1){
		scanf("%d %d",&m,&n);
		if(n+m==0)break;
		memset(fie,0,sizeof(fie));
		for(int i=0;i<n;i++){
			string a;
			cin >> a;
			if(a[0]=='A'){
				for(int j=0;j<m;j++){
					if(fie[j]==0){
						fie[j]=1;
						break;
					}
				}
			}
			if(a[0]=='B'){
				int j;
				for(j=m-1;j>=0;j--){
					if(j>0 && fie[j-1]==1)continue;
					if(j<m-1 && fie[j+1]==1)continue;
					if(fie[j]==0){
						fie[j]=2;
						break;
					}
				}
				if(j==-1){
					for(int j=0;j<m;j++){
						if(fie[j]==0){
							fie[j]=2;
							break;
						}
					}
				}
			}
			if(a[0]=='C'){
				if(i==0){
					if(n%2==1)fie[(n+1)/2]=3;
					if(n%2==0)fie[n/2+1]=3;
				}else{
					for(int j=0;j<m;j++){
						if(fie[j]!=0){
							if(j<m-1 && fie[j+1]==0){
								fie[j+1]=3;
								break;
							}
							if(j>0 && fie[j-1]==0){
								fie[j-1]=3;
								break;
							}
						}
					}
				}
			}
			if(a[0]=='D'){
				if(i==0){
					fie[0]=4;
				}else{
					for(int j=0;j<m;j++)dist[j]=101;
					for(int j=0;j<m;j++){
						if(fie[j]!=0){
							for(int k=0;k<m;k++){
								dist[k]=min(dist[k],abs(k-j));
							}
						}
					}
					int lll=0;
					for(int j=0;j<m;j++){
						if(dist[j]>dist[lll])lll=j;
					}
					fie[lll]=4;
				}
			}
		}
		for(int i=0;i<m;i++){
			printf("%c",data[fie[i]]);
		}
		printf("\n");
	}
	return 0;
}