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>

int n, m;
int chair[105];

int dist(int k){
	int ret = 1000;
	for(int i = k; i <= n; ++i){
		if(chair[i]){
			ret = i - k;
		}
	}
	for(int i = k; i >= 1; --i){
		if(chair[i]){
			ret = std::min(ret, k - i);
		}
	}
	return ret;
}

int main(){
	while(true){
		for(int i = 0; i < 105; ++i)chair[i] = 0;
		
		std::cin >> n >> m;
		if(n == 0 && m == 0)break;

		for(int i = 0; i < m; ++i){
			char ch;
			std::cin >> ch;

			if(ch == 'A'){
				for(int j = 1; j <= n; ++j){
					if(chair[j] == 0){
						chair[j] = 1;
						break;
					}
				}
			}
			else if(ch == 'B'){
				bool f = false;

				for(int j = n; j >= 1; --j){
					if(chair[j] == 0 && chair[j - 1] != 1 && chair[j + 1] != 1){
						chair[j] = 2;
						f = true;
						break;
					}
				}

				if(!f){
					for(int j = 1; j <= n; ++j){
						if(chair[j] == 0){
							chair[j] = 2;
							break;
						}
					}
				}
			}
			else if(ch == 'C'){
				if(i == 0)chair[n % 2 ? ((n + 1) / 2) : (n / 2 + 1)] = 3;
				else{
					for(int j = 1; j <= n; ++j){
						if(chair[j]){
							if(j + 1 <= n && chair[j + 1] == 0){
								chair[j + 1] = 3;
								break;
							}
							if(j - 1 >= 1 && chair[j - 1] == 0){
								chair[j - 1] = 3;
								break;
							}
						}
					}
				}
			}
			else if(ch == 'D'){
				if(i == 0)chair[1] = 4;
				else{
					int maxV = -1000, maxI;
					for(int j = 1; j <= n; ++j){
						if(chair[j] == 0){
							if(dist(j) > maxV)maxV = dist(j), maxI = j;
						}
					}
					chair[maxI] = 4;
				}
			}
		}

		for(int i = 1; i <= n; ++i){
			if(chair[i] == 0)std::cout << "#";
			else std::cout << (char)('A' + chair[i] - 1);
		}
		std::cout << std::endl;
	}
	
	return 0;
}

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';
				break;
		}
	}
	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] == '#'){
			ans = k;
			break;
		}
	}
	for(int k=ans; k<n; k++){
		if(chr[k] != '#')
			continue;
		tmp1=0;
		tmp2=0;
		if(k<n-1){
			for(int t=k+1; t<n; t++){
				if(chr[t] != '#')
					break;
				tmp1++;
				if(t == n-1)
					tmp1 = n+1;
			}
		}
		else
			tmp1 = n+1;
		if(k>0){
			for(int t=k-1; t>=0; t--){
				if(chr[t] != '#')
					break;
				tmp2++;
				if(t == 0)
					tmp2 = n+1;
			}
		}
		else
			tmp2 = n+1;
		if(tmp1 > tmp2)
			tmp1 = tmp2;
		if(tmp1 > tmp){
			tmp = tmp1;
			ans = k;
		}
		std::cout << tmp1 << ' ';
	}
	std::cout << '\n';
	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)
				chr[i] = '#';
			else
				std::cin >> peo[i];
		}
		solve();
		delete[] chr;
		delete[] peo;
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

#define MAX 10000
char C[MAX + 2];
int n, m;
void setLeft(char ch) {
	for (int i = 1;; i++) {
		if (C[i] == '#') {
			C[i] = ch;
			return;
		}
	}
}
void setB() {
	for (int i = n; i >= 1; i--) {
		if (C[i] == '#' && C[i - 1] != 'A' && C[i + 1] != 'A') {
			C[i] = 'B';
			return;
		}
	}
	setLeft('B');
}
bool isEmpty() {
	for (int i = 1; i <= n; i++)
		if (C[i] != '#')
			return false;
	return true;
}
void setC() {
	if (isEmpty()) {
		C[n / 2 + 1] = 'C';
		return;
	}
	for (int i = 1; i <= n; i++) {
		if (C[i] == '#')
			continue;
		if (C[i + 1] == '#') {
			C[i + 1] = 'C';
			return;
		}
		if (C[i - 1] == '#') {
			C[i - 1] = 'C';
			return;
		}
	}
}
int getDist(int p) {
	int l = 0, r = 0;
	while (C[p + l - 1] == '#')
		l--;
	if (C[p + l - 1] == 'X')
		l = -1000000;
	while (C[p + r + 1] == '#')
		r++;
	if (C[p + r + 1] == 'X')
		r = 1000000;
	return min((-1) * l, r);
}
void setD() {
	if (isEmpty()) {
		C[1] = 'D';
		return;
	}
	int d, mi, md = -1;
	for (int i = 1; i <= n; i++) {
		if (C[i] != '#')
			continue;
		d = getDist(i);
		if (d > md) {
			md = d;
			mi = i;
		}
	}
	C[mi] = 'D';
}
main() {
	char ch;
	while( cin >> n >> m && n && m ) {
		for(int i = 0;i<=n+1;i++) C[i] = '#';
		C[0] = C[n+1] = 'X';
		for(int i = 1;i<=m;i++) {
			cin >> ch;
			if ( ch == 'A' ) setLeft('A');
			else if ( ch == 'B' ) setB();
			else if ( ch == 'C' ) setC();
			else if ( ch == 'D' ) setD();
		}
		for(int i = 1;i<=n;i++) cout << C[i];
		cout << endl;
	}
}