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
		}
		chairs := make([]string, n)
		for i := range chairs {
			chairs[i] = "#"
		}
		sit := func(who string) {
			if who == "A" {
				chairs[getStringIndex(chairs, "#")] = "A" // A国の人は左から見て行って空いている席を見つけ次第座る
				// log.Println(chairs)
			} else if who == "B" {
				f := true
				for i := n-1; i > -1; i-- {
					// B国の人はA国人の隣以外で、右端から空いている椅子に座る
					if chairs[i] == "#" && (i == 0 || chairs[i-1] != "A") && (i == n-1 || chairs[i+1] != "A") {
								chairs[i] = "B"
								f = false
								break
					}
				}
				// A国人の隣しか空いていない場合、我慢して左端から空いている椅子に座る
				if f {
					chairs[getStringIndex(chairs, "#")] = "B"
				}
				// log.Println(chairs)
			} else if who == "C" { // C国人は人の隣に座りたい
				for i := 0; i < n; i++ {
					if chairs[i] != "#" {
						if i + 1 <= n-1 && chairs[i+1] == "#" {
							chairs[i+1] = "C"
							break
						} else if i - 1 >= 0 && chairs[i-1] == "#" {
							chairs[i-1] = "C"
							break
						}
					}
				}
				// log.Println(chairs)
			} else { // who == "D"
				// D国の人は人から離れて座りたい
				// どうしても誰かの隣に座らなければならない場合、その中で一番左側にある椅子に座る
				scores := make([]int, n)
				for i := range scores {
					scores[i] = INF
				}
				for i, v := range chairs {
					if v == "#" {
						scores[i]++
					}
				}
				for i := n-1; i > -1; i-- {
					tmp := 0
					if chairs[i] == "#" {
						tmp++
					} else {
						tmp = 0
					}
					scores[i] = min(scores[i], tmp)
				}
				chairs[getIntIndex(scores, getMax(scores))] = "D"
				// log.Println(chairs)
			}
		}
		scanner.Scan()
		if first := scanner.Text(); first == "A" || first == "D" {
			chairs[0] = first
		} else if first == "B" {
			chairs[len(chairs)-1] = "B"
		} else {
			chairs[n/2] = "C"
		}
		// log.Println(chairs)
		for i := 0; i < m-1; i++ {
			scanner.Scan()
			sit(scanner.Text())
		}
		fmt.Println(strings.Join(chairs, ""))
	}
}

func getStringIndex(chairs []string, who string) int {
	for i, v := range chairs {
		if v == who {
			return i
		}
	}
	return -1
}

func getIntIndex(scores []int, target int) int {
	for i, v := range scores {
		if v == target {
			return i
		}
	}
	return -1
}

func min(a, b int) int {
	if a > b {
		return b
	}
	return a
}

func getMax(scores []int) int {
	tmp := -1
	for _, v := range scores {
		if tmp < v {
			tmp = v
		}
	}
	return tmp
}

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 maxIndex = -1, dist = -1;
		for (int i = 0; i < n; ++i) {
			if(map[i] != '#')continue;
			int right = 0;
			if(i == n-1)right = n;
			for(int j = i+1; j < n; ++j) {
				if (map[j] == '#')++right;
				else break;
			}
			int left = 0;
			if (i == 0)left = n;
			for (int j = i-1; j >= 0; --j) {
				if (map[j] == '#')++left;
				else break;
			}
			if (dist < min(right, left)) {
				maxIndex = i;
			    dist = min(right, left);
			}
		}
		map[maxIndex] = '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<iostream>
#include<algorithm>
#include<vector>

using namespace std;

class A {
public:
	vector<char> set_chair(vector<char> chair) {
		for (int i = 1; i < chair.size()-1; i++) {
			if (chair[i] == '#') {
				chair[i] = 'A';
				return chair;
			}
		}
	}
};

class B {
public:
	vector<char> set_chair(vector<char> chair) {
		for (int i = chair.size()-2; i >= 1; i--) {
			if (chair[i] == '#' && chair[i + 1] != 'A' && chair[i - 1] != 'A') {
				chair[i] = 'B';
				return chair;
			}
		}
		for (int i = 1; i < chair.size()-1; i++) {
			if (chair[i] == '#') {
				chair[i] = 'B';
				return chair;
			}
		}
	}
};

class C {
public:
	vector<char> set_chair(vector<char> chair) {
		for (int i = 1; i < chair.size()-1; i++) {
			if (chair[i] != '#') {
				if (chair[i + 1] == '#' && i+1 != chair.size()-1) {
					chair[i + 1] = 'C';
					return chair;
				}else if (chair[i - 1] == '#' && i-1 != 0) {
					chair[i - 1] = 'C';
					return chair;
				}
			}
		}

		if (chair.size() % 2 == 1)chair[(chair.size() + 1) / 2 + 1] = 'C';
		else chair[chair.size() / 2 + 1 + 1] = 'C';
		return chair;

	}
};

class D {
public:
	vector<char> set_chair(vector<char> chair) {
		vector<int> numOfMostDistance(chair.size());
		for (int i = 1; i < chair.size() - 1; i++) {
			int rightMax = 0;
			int leftMax =  0;
			for (int j = 0; chair[i + j] == '#' && j+i != chair.size()-1; rightMax++,j++);
			for (int j = 0; chair[i - j] == '#' && i-j != 0; leftMax++,j++);
			numOfMostDistance[i] = min(rightMax, leftMax);
		}

		bool chairIsEmpty = true;
		for (int i = 1; i < chair.size() - 1; i++) {
			if (chair[i] != '#')chairIsEmpty = false;
		}

		if (chairIsEmpty)chair[1] = 'D';
		else chair[max_element(numOfMostDistance.begin(), numOfMostDistance.end()) - numOfMostDistance.begin()] = 'D';
		return chair;
	}
};


int main() {
	int n, m;
	while (cin >> n >> m, n, m) {
		vector<char> chair(n + 2,'#');
		for (int i = 0; i < m; i++) {
			char a; cin >> a;
			if (a == 'A') {
				A tmp;
				chair = tmp.set_chair(chair);
			}
			if (a == 'B') {
				B tmp;
				chair = tmp.set_chair(chair);
			}
			if (a == 'C') {
				C tmp;
				chair = tmp.set_chair(chair);
			}
			if (a == 'D') {
				D tmp;
				chair = tmp.set_chair(chair);
			}
		}
		for (int i = 1; i < chair.size() - 1; i++)cout << chair[i];
		cout << endl;
	}
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
vector<int> data;
int n,N;

int getLeft(){
	rep(i,n)if(data[i] == 0)return i;
	return -1;
}

int B(){
	for(int i=n-1;i>=0;i--){
		if(data[i] == 0 && data[i+1] != 1 && data[i-1] != 1)return i;
	}
	return getLeft();
}
int C(){
	bool f = true;
	rep(i,N)f &=(data[i+1]==0);
	if(f)return (N&1?n/2:N/2+1);
	
	rep(i,n){
		if(data[i] && data[i] != -1){
			if(data[i+1]==0)return i+1;
			else if(data[i-1]==0)return i-1;
		}
	}
}

int most(int pos,int a){
	int i = 0;
	while(!data[pos+i*a]){
		i++;
		if(data[pos+i*a] == -1)return 999999;
	}
	return i;
}

int D(){
	int good , val = -1;
	rep(i,n){
		if(data[i] == 0){
			int t = min( most(i,-1) , most(i,1) );
			if(t > val){
				val = t;
				good = i;
			}
		}
	}
	return good;
}
int main(){
	string tab = "#ABCD";
	int m;
	while(cin >> n >> m , n ){
		N = n ; n++;
		data.resize(N+2);
		fill(data.begin(),data.end(),0);
		data[0] = -1 , data[n] = -1;
		
		rep(i,m){
			char c; cin >> c;
			switch(c){
			case 'A':
				data[getLeft()] = 1;
				break;
			case 'B':
				data[B()] = 2;
				break;
			case 'C':
				data[C()] = 3;
				break;
			case 'D':
				data[D()] = 4;
				break;
			}
		}
		rep(i,N){
			int t = data[i+1];
			cout << tab[t];
		}
		cout << endl;
	}
}