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>

char *chr, *peo;
int n,m;

void sitA(int i){
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'A';
			return;
		}
	}
}

void sitB(int i){
	if(chr[n-1] == '#' && chr[n-2] != 'A'){
		chr[n-1] = 'B';
		return;
	}
	for(int k=n-2; k>0; k--){
		if(chr[k] == '#' && chr[k-1] != 'A' && chr[k+1] != 'A'){
			chr[k] = 'B';
			return;
		}
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#'){
			chr[k] = 'B';
			return;
		}
	}
}

void sitC(int i){
	if(i==0){
		if(n%2 == 0)
			chr[n/2] = 'C';
		else
			chr[(n-1)/2] = 'C';
		return;
	}
	for(int k=0; k<n; k++){
		if(chr[k] == '#')
			continue;
		if(k<n-1){
			if(chr[k+1] == '#'){
				chr[k+1] = 'C';
				return;
			}
		}
		if(k>0){
			if(chr[k-1] == '#'){
				chr[k-1] = 'C';
				return;
			}
		}
	}
}

void sitD(int i){
	if(i==0){
		chr[0] = 'D';
		return;
	}
	int ans,tmp=0,tmp1,tmp2;
	for(int k=0; k<n; k++){
		if(chr[k] != '#')
			continue;
		tmp1=0;
		tmp2=0;
		for(int t=k; t<n; t++){
			if(chr[t] != '#')
				break;
			tmp1++;
			if(t == n-1)
				tmp1 = n+1;
		}
		if(k == n-1)
			tmp1 = n+1;
		for(int t=k; t>=0; t--){
			if(chr[t] != '#')
				break;
			tmp2++;
			if(t == 0)
				tmp2 = n+1;
		}
		if(k == 0)
			tmp2 = n+1;
		if(tmp1 > tmp2)
			tmp1 = tmp2;
		if(tmp1 > tmp){
			tmp = tmp1;
			ans = k;
		}
	}
	chr[ans] = 'D';
}

void solve(){
	char tmp;
	for(int i=0; i<m; i++){
		tmp = peo[i];
		switch(tmp){
		case 'a':
		case 'A':
			sitA(i);
			break;
		case 'b':
		case 'B':
			sitB(i);
			break;
		case 'c':
		case 'C':
			sitC(i);
			break;
		case 'd':
		case 'D':
			sitD(i);
			break;
		}
	}
	std::cout << chr << std::endl;
}

int main(){
	while(true){
		std::cin >> n >> m;
		if(!n && !m)
			return 0;
		chr = new char[n];
		peo = new char[m];
		for(int i=0; i<n; i++){
			chr[i] = '#';
			if(i<m)
				std::cin >> peo[i];
		}
		solve();
		delete[] chr;
		delete[] peo;
	}
}

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);
	}
}

C++: #include<iostream>
#include<vector>
#include<string>
#include<cstring>
#include<algorithm>
#include<map>
#include<set>
#include<cmath>
#include<cassert>
#include<queue>

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;

int ans[111];

int calc(int x, int n) {
	int l = 0;
	for (; l <= x; l++) {
		if (ans[x-l] != -1) break;
	}
	if (l == x+1) l = n;
	int r = 0;
	for (; r+x < n; r++) {
		if (ans[r+x] != -1) break;
	}
	if (r+x == n) r = n;
	return min(l, r);
}

int main() {
	int N, M;
	while (cin >> N >> M) {
		if (N == 0 && M == 0) break;
		memset(ans, -1, sizeof(ans));
		for (int t = 0; t < M; t++) {
			char c;
			cin >> c;
			if (c == 'A') {
				for (int i = 0; i < N; i++) {
					if (ans[i] == -1) {
						ans[i] = 0;
						break;
					}
				}
			}
			if (c == 'B') {
				bool done = false;
				for (int i = N-1; i >= 0; i--) if (ans[i] == -1) {
					if (ans[i+1] != 0) {
						if (i == 0 || ans[i-1] != 0) {
							done = true;
							ans[i] = 1;
							break;
						}
					}
				}
				if (!done) {
					for (int i = 0; i < N; i++) {
						if (ans[i] == -1) {
							ans[i] = 1;
							break;
						}
					}
				}
			}
			if (c == 'C') {
				if (t == 0) {
					ans[(N+1)/2] = 2;
				} else {
					for (int i = 0; i < N; i++) {
						if (ans[i] != -1 && ans[i+1] == -1) {
							ans[i+1] = 2;
							break;
						}
					}
				}
			}
			if (c == 'D') {
				if (t == 0) {
					ans[0] = 3;
				} else {
					int index = 0, maxi = 0;
					for (int i = 0; i < N; i++) if (ans[i] == -1) {
						int tmp = calc(i, N);
						if (tmp > maxi) {
							maxi = tmp;
							index = i;
						}
					}
					ans[index] = 3;
				}
			}
		}
		for (int i = 0; i < N; i++) {
			if (ans[i] == 0) cout << 'A';
			else if (ans[i] == 1) cout << 'B';
			else if (ans[i] == 2) cout << 'C';
			else if (ans[i] == 3) cout << 'D';
			else cout << '#';
		}
		cout << endl;
	}
	return 0;
}