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;
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=1000;
          if(i==0)p2=1000;
          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 max=0,x=0,res=0;
		for(a=0;a<n;a++){
			if(a==n-1 && map[a]=='#'){
				if(res>max){
					x=a;
					max=res;
				}
			}else if(map[a]=='#'){
				res++;
			}else{
				if((res+1)/2>max){
					if(res%2==0)x=a-res/2-1;
					if(res%2==1)x=a-(res+1)/2;
					max=res;
				}
				ch=true;
				res=0;
			}
		}
		if(ch){
			map[x]='D';
		}else{
			map[0]='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;
}

C++: #include<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<n;i++)
using namespace std;

char s[200], a[2];
int main() {
	bool b;
	int n, m;
	while (scanf("%d%d", &n, &m), n) {
		memset(s, 0, sizeof(s)); rep(i, n)s[i] = '#';
		rep(i, m) {
			scanf("%s", a);
			switch (a[0]) {
			case 'A':
				rep(i, n) { if (s[i] == '#') { s[i] = 'A'; break; } }
				break;
			case 'B':
				b = false;
				for (int i = n - 1; i >= 0; i--) {
					if (s[i] == '#' && (!i || s[i - 1] != 'A') && (i + 1 >= n || s[i + 1] != 'A')) {
						b = true; s[i] = 'B'; break;
					}
				}
				if (!b)rep(i, n) { if (s[i] == '#') { s[i] = 'B'; break; } }
				break;
			case 'C':
				b = false;
				rep(i, n) {
					if (s[i] != '#') {
						if (i + 1 < n&&s[i + 1] == '#') { s[i + 1] = 'C'; b = true; break; }
						if (i&&s[i - 1] == '#') { s[i - 1] == 'C'; b = true; break; }
					}
				}
				if (!b)s[n & 1 ? (n + 1) / 2 : n / 2 + 1] = 'C';
				break;
			case 'D':
				int k, Max = -1;
				rep(i, n) {
					if (s[i] != '#')continue;
					int cnt = INT_MAX;
					int t = i - 1;
					for (; t >= 0 && s[t] == '#'; t--);
					cnt = t == -1 ? INT_MAX : i - t;
					t = i + 1;
					for (; t < n&&s[t] == '#'; t++);
					cnt = min(cnt, t == n ? INT_MAX : t - i);
					if (Max < cnt) {
						k = i; Max = cnt;
					}
				}
				s[k] = 'D';
				break;
			}
		}
		printf("%s\n", s);
	}
}