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[:len(chair)-1], ""))
	}
}

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>
#include<string.h>
#include<cstdio>
using namespace std;
int main() {
	int n, m, temp;
	char str, str2[10001], str3[10001] = { NULL };
	while (1) {
		cin >> n >> m;
		if (n == 0 && m == 0)return 0;
		for (int i = 0; i < m; i++) {
			cin >> str2[i];
		}
		for (int i = 0; i < n; i++) {
			str3[i] = '#';
		}
		for (int i = 0; i < m; i++) {
			if (str2[i] == 'A') {
				for (int j = 0; j < n; j++) {
					if (str3[j] == '#') {
						str3[j] = 'A';
						goto end;
					}
				}
			}
			else if (str2[i] == 'B') {
				for (int j = n - 1; j > 0; j--) {
					if (str3[j] == '#'&&str3[j - 1] != 'A'&&str3[j + 1] != 'A') {
						str3[j] = 'B';
						temp++;
						goto end;
					}
				}
				if (temp == 0) {
					for (int j = 0; j < n; j++) {
						if (str3[j] == '#') {
							str3[j] = 'B';
							temp++;
							goto end;
						}
					}
				}
				if (temp == 0) {
					for (int j = 0; j < n; j++) {
						if (str3[j] == '#') {
							str3[j] = 'B';
							goto end;
						}
					}
				}
				temp = 0;
			}
			else if (str2[i] == 'C') {
				for (int j = 0; j < n; j++) {
					if (str3[j] != '#' ) {
						if (str3[j + 1] == '#') {
							str3[j + 1] = 'C';
							temp++;
							goto end;
						}
					}
				}
				if (temp == 0) {
					if (n % 2 == 0)temp = n / 2 + 1;
					else temp = (n + 1) / 2;
					str3[temp] = 'C';
				}
				temp = 0;
			}
			else if (str2[i] == 'D') {
				temp = 0;
				int gun = 0, x, y,r=0;
				for (int j = 0; j < n; j++) {
					int  q = 0, w = 0,f=0;
					if (str3[j] == '#') {
						x = y = j;
						while (1) {
							x++;
							y--;
							if (x <= n&&y > 0) {
								if (str3[x] == '#' && str3[y] == '#') {
									f++;
									temp++;
									if(r<f)
									str3[j] = 'D';
									if (r != 0) {
										str3[f] = '#';
									}
									r = f;
								}
							}
							else {
								break;
							}
						}
						x = y = j;
						while (temp==0) {
							x++;
							y--;
							if (x <= n || y > 0) {
								if (str3[x] == '#' &&x <= n) {
									q++;
									if (gun < q && gun>0) {
										str3[x] = 'D';
										str3[gun] = '#';
										gun = q;
										temp++;
									}
								}
								if (str3[y] == '#' &&y > 0) {
									w++;
									if (gun < w&& gun>0) {
										str3[y] = 'D';
										str3[gun] = '#';
										gun = w;
										temp++;
									}
								}
							}
							else {
								goto loop;
							}
						}
					}
				}
			loop:
				if (temp == 0) {
					for (int j = 0; j < n; j++) {
						if (str3[j] == '#') {
							str3[j] = 'D';
							goto end;
						}
						if (j == n - 1) {
							str3[0] = 'D';
						}
					}
				}
				temp = 0;
			}
		end:;
			/*for (int i = 0; i < n; i++) {
				cout << str3[i];
			}
			cout << endl;*/
		}
		for (int i = 0; i < n; i++) {
			cout << str3[i];
		}
		cout << endl;
		memset(str3, NULL, sizeof(str3));
		memset(str2, NULL, sizeof(str2));
		temp = 0;
	}
}

C++: #include<bits/stdc++.h>
using namespace std;
int main()
{
	int N,M;
	while(true){
		scanf("%d%d",&N,&M);
		if(N==0&&M==0)return 0;
		int seats[10009];
		for(int i=0;i<10009;i++){
			seats[i]=0;
		}
		
		for(int i=0;i<M;i++){
			string S;
			cin >> S;
			if(S[0]=='A'){
				for(int j=0;j<N;j++){
					if(seats[j]==0){
						seats[j]=1;
						break;
					}
				}
			}
			else if(S[0]=='B'){
				bool F=true;
				for(int j=N-1;j>=0;j--){
					if(F&&(j==0||seats[j-1]!=1)&&(j==N-1||seats[j+1]!=1)&&seats[j]==0){
						seats[j]=2;F=false;
					}
				}
				if(F){
					for(int j=0;j<N;j++){
						if(seats[j]==0){
							seats[j]=2;
							break;
						}
					}
				}
			}
			else if(S[0]=='C'){
				bool F=true;
				for(int j=0;j<N;j++){
					if(seats[j]!=0){
						if(F&&j!=N-1&&seats[j+1]==0){
							seats[j+1]=3;F=false;
						}
						else if(F&&j!=0&&seats[j-1]==0){
							seats[j-1]=3;F=false;
						}
					}
					if(!F)break;
				}
				if(F)seats[N/2]=3;
			}
			else{
				int maxd=-1,maxi;
				bool F=true;
				for(int i=0;i<N;i++){
					if(seats[i]!=0)F=false;
				}
				if(F){
					seats[0]=4;
					continue;
				}
				for(int i=0;i<N;i++){
					int d=0;
					if(seats[i]!=0)d=-114;
					int l=i;int r=i;
					while(l>=0&&seats[l]==0&&r<N&&seats[r]==0){
						d++;
						l--;
						r++;
					}
					if(maxd<d){
						maxd=d;
						maxi=i;
					}
					
				}
				seats[maxi]=4;
			}
			
		}
		for(int i=0;i<N;i++){
				if(seats[i]==0)printf("#");
				if(seats[i]==1)printf("A");
				if(seats[i]==2)printf("B");
				if(seats[i]==3)printf("C");
				if(seats[i]==4)printf("D");
			}
			printf("\n");
	}
}