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 main(){

  int n,m;
  int j;
  char chair[100];
  char p;
  int left,max,m_left;

  while(1){

    cin >> n >> m;
    if(n==0 && m==0)
      break;

    for(int i=0; i<n; i++)
      chair[i]='#';


    for(int i=0; i<m; i++){

    cin >> p;

    if(p=='A'){
      j=0;
      while(chair[j]!='#')
	j++;

      chair[j]='A';
    }///////////////////////A

    else if(p=='B'){
      j=n-1;
      while(1){
	if(chair[j]=='#'){
	  if(j==n-1 && chair[j-1]!='A')
	    break;

	  else if(j>0 && chair[j+1]!='A' && chair[j-1]!='A')
	    break;

	  else if(chair[j+1]!='A')
	    break;
	  
	  else{
	    j=-1;
	    break;
	  }
	}
      }

      if(j!=-1)
	chair[j]='B';

      else{
	j=0;
	while(chair[j]=='#')
	  j++;

	chair[j]='B';
      }

    }////////////////////////B


    else if(p=='C'){
      j=0;
      while(1){
	if(chair[j]!='#'){
	  if(chair[j+1]=='#'&&j!=n-1){
	    j++;
	    break;
	  }
	  else if(j!=0 && chair[j-1]=='#'){
	    j--;
	    break;
	  }
	}

	if(j==n-1){
	  j=-1;
	  break;
	}

	j++;
      }

      if(j==-1){
	if(n%2==1)
	  j=(n+1)/2;
	else
	  j=n/2+1;
      }

      chair[j] = 'C';
    }///////////////////////C


    else{
      left=0; max=1; m_left=0;
      j=1;
      while(j<=n-1){
	if(chair[j]!='#'){
	  left=j;
	  j++;
	}

	if(max < j-left){
	  max = j-left;
	  m_left = left;
	}
	j++;
      }

      if(max == 1)
	j = m_left+1;

      else if(max == n-1)
	j=0;

      else{
	if(max%2==1)
	  j=m_left+max/2 +1;
	else
	  j=m_left+max/2;
      }


      chair[j]='D';

    }///////////////////////D

    }


    for(int i=0; i<n; i++)
      cout << chair[i];


    cout << endl;

  }


  return 0;

}

C++: #include<iostream>
#include<string>
using namespace std;
int main(){
  int n,m;
  while(cin >>n>>m,n||m){
    int row[100] = {0},chair[102] = {0};
    for(int i=0; i<m; i++){
      string s;
      cin >>s;
      if(s == "A"){row[i] = 1;}
      if(s == "B"){row[i] = 2;}
      if(s == "C"){row[i] = 3;}
      if(s == "D"){row[i] = 4;}
    }
    for(int i=0; i<m; i++){
      if(row[i] == 1){
	for(int j=0; j<n; j++){
	  if(!chair[j+1]){
	    chair[j+1] = 1;
	    break;
	  }
	}
      }
      if(row[i] == 2){
	bool non = true;
	for(int j=n-1; j>=0; j--){
	  if(chair[j] != 1 && chair[j+1] == 0 && chair[j+2] != 1){
	    chair[j+1] = 2;
	    non = false;
	    break;
	  }
	}
	if(non){
	  for(int j=0; j<n; j++){
	    if(!chair[j+1]){
	      chair[j+1] = 2;
	      break;
	    }
	  }
	}
      }
      if(row[i] == 3){
	if(!i){
	  if(n%2){chair[(n+1)/2] = 3;}
	  else{chair[n/2+1] = 3;}
	}
	else{
	  for(int j=1; j<=n; j++){
	    if(chair[j] && !chair[j+1] && j < n-1){
	      chair[j+1] = 3;
	      break;
	    }
	    if(chair[j] && !chair[j-1] && j > 1){
	      chair[j-1] = 3;
	      break;
	    }
	  }
	}
      }
      if(row[i] == 4){
	if(!i){chair[1] = 4;}
	else{
	  int r = 0,s = -1;
	  bool non = true;
	  for(int j=0; j<n; j++){
	    if(!chair[j+1]){
	      int x = 200;
	      for(int k=j+1; k<n; k++){
		if(chair[k+1]){
		  if(x > k-j){x = k-j;}
		  break;
		}
	      }
	      for(int k=j-1; k>=0; k--){
		if(chair[k+1]){
		  if(x > j-k){x = j-k;}
		  break;
		}
	      }
	      if(r < x){r = x;s = j;}
	    }
	  }
	  if(s != -1){
	    chair[s+1] = 4;
	    non = false;
	  }
	  if(non){
	    for(int j=0; j<n; j++){
	      if(!chair[j+1]){
		chair[j+1] = 4;
		break;
	      }
	    }
	  }
	}
      }
    }
    for(int i=0; i<n; i++){
      if(chair[i+1] == 0){cout <<"#";}
      if(chair[i+1] == 1){cout <<"A";}
      if(chair[i+1] == 2){cout <<"B";}
      if(chair[i+1] == 3){cout <<"C";}
      if(chair[i+1] == 4){cout <<"D";}
    }
    cout <<endl;
  }
  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;
				}
			}
		}
	}
	else if (who == 3) {
		for (int i = 1; i < seats.size(); ++i) {
			if (seats[i - 1]) {
				if (!seats[i]) {
					seats[i] = who;
					return;
				}
			}
		}
		seats[seats.size() / 2] = who;
	}
	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;
	}
}

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;
}