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++: #define _USE_MATH_DEFINES
#include<cstdio>
#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#include<stack>
#include<cmath>
#include<climits>
using namespace std;

int N, M;
char C;
char chairs[102];

void PutA(){
	for(int i = 1; i <= N; i++){
		if(chairs[i] == '#'){
			chairs[i] = 'A';
			return;
		}
	}
}

void PutB(){
	for(int i = N; i >= 1; i--){
		if(chairs[i+1] != 'A' && chairs[i] == '#' && chairs[i-1] != 'A'){
			chairs[i] = 'B';
			return;
		}
	}
	for(int i = 1; i <= N; i++){
		if(chairs[i] == '#'){
			chairs[i] = 'B';
			return;
		}
	}
}

void PutC(){
	for(int i = 1; i <= N; i++){
		if(chairs[i] != '#'){
			if(chairs[i+1] == '#'){
				chairs[i+1] = 'C';
				return;
			}
			if(chairs[i-1] == '#'){
				chairs[i-1] = 'C';
				return;
			}
		}
	}
	if(N&1) chairs[ (N+1)/2 ] = 'C';
	chairs[N/2 + 1] = 'C';
}

void PutD(){
	int l[102], r[102];
	l[0] = INT_MAX/2; r[N+1] = INT_MAX/2;
	for(int i = 1; i <= N; i++) l[i] = (chairs[i] == '#') ? l[i-1] + 1 : 0;
	for(int i = N; i >= 1; i--) r[i] = (chairs[i] == '#') ? r[i+1] + 1 : 0;

	int ma_idx, ma_d = -1;
	for(int i = 1; i <= N; i++){
		int d = min(l[i], r[i]);
		if(d >= INT_MAX/2) d = INT_MAX;
		if(ma_d < d){
			ma_idx = i; ma_d = d;
		}
	}
	chairs[ma_idx] = 'D';
}

int main(){
	void (*put[4])() = {PutA, PutB, PutC, PutD};

	while(cin >> N >> M, N || M){
		fill_n(chairs, N+2, '#');
		chairs[0] = chairs[N+1] = '.';
		for(int i = 0; i < M; i++){
			cin >> C;
			put[C - 'A']();
			//for(int i = 1; i <= N; i++) printf("%c", chairs[i]); puts("");
		}
		for(int i = 1; i <= N; i++) printf("%c", chairs[i]); puts("");
	}
	return 0;
}

C++: #include <iostream>
#include <cstdlib>
#include <string>
using namespace std;

char chair[128];
int n, m;
const int M = 2;

void A() {
	for(int i = 0; i < n; i++) {
		if(chair[i+M] == 'N') {
			chair[i+M] = 'A';
			break;
		}
	}
}

void B() {
	for(int i = n-1; i >= 0; i--) {
		if(chair[i+M] == 'N' && chair[i+1+M] != 'A' && chair[i-1+M] != 'A') {
			chair[i+M] = 'B';
			return;
		}
	}
	for(int i = 0; i < n; i++) {
		if(chair[i+M] == 'N') {
			chair[i+M] = 'B';
			return;
		}
	}
}

void C() {
	for(int i = 0; i < n; i++) {
		if(chair[i+M] != 'N') {
			if(chair[i+1+M] == 'N') {
				chair[i+1+M] = 'C';
				return;
			}
			else if(chair[i-1+M] == 'N') {
				chair[i-1+M] = 'C';
				return;
			}
		}
	}
	chair[n/2+M] = 'C';
}

void D() {
	int mx = 0;
	int indx = 0;
	for(int i = 0; i < n; i++) {
		if(chair[i+M] == 'N') {
			int mn = 1000;
			for(int j = 0; j < n; j++) {
				if(chair[j+M] != 'N') {
					if(mn > abs(j - i))
						mn = abs(j - i);
				}
			}
			if(mn > mx) {
				mx = mn;
				indx = i;
			}
		}
	}
	chair[indx+M] = 'D';
}

int main() {
	while(cin >> n >> m, n || m) {
		for(int i = 0; i < 128; i++)
			chair[i] = 'N';
		for(int i = 0; i < m; i++) {
			string s;
			cin >> s;
			if(s[0] == 'A')
				A();
			else if(s[0] == 'B')
				B();
			else if(s[0] == 'C')
				C();
			else
				D();
		}
		for(int i = 0; i < n; i++) {
			cout << (chair[i+M] == 'N' ? '#' : chair[i+M]);
		}
		cout << endl;
	}
}

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 (s[i] == '#' && (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;
			}
		}
	}
	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;
}