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 "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
const ld eps = 1e-9;

//// < "d:\d_download\visual studio 2015\projects\programing_contest_c++\debug\a.txt" > "d:\d_download\visual studio 2015\projects\programing_contest_c++\debug\b.txt"

void sit(vector<int>&seats, int who) {
	if (who == 1) {
		for (int i = 0; i < seats.size(); ++i) {
			if (!seats[i]) {
				seats[i] = who;
				return;
			}
		}
	}
	else if (who == 2) {
		for (int i = seats.size()-1; i >= 0; --i) {
			if (!seats[i]) {
				bool ok = true;
				for (int k = i+1; k >= i-1; k -= 2) {
					if (k >= 0 && k < seats.size()) {
						if (seats[k] == 1)ok = false;
					}
				}
				if (ok) {
					seats[i] = who;
					return;
				}
			}
		}
		for (int i = 0; i < seats.size(); ++i) {
			if (!seats[i]) {
				seats[i] = who;
				return;
			}
		}
	}
	else if (who == 3) {
		for (int i = 0; i < seats.size(); ++i) {
			if (seats[i]) {
				if (i!=seats.size()-1&&!seats[i+1]) {
					seats[i+1] = who;
					return;
				}
				else if (i != 0 && !seats[i - 1]) {
					seats[i - 1] = who;
					return;
				}
			}
		}
		seats[seats.size() / 2] = who;
		return;
	}
	else {
		vector<int>diss(seats.size(), 1000);
		for (int i = 0; i < seats.size(); ++i) {
			if (seats[i]) {
				diss[i] = 0;
				for (int j = i - 1; j >= 0; --j) {
					diss[j] = min(diss[j], i-j);
				}
				for (int j = i + 1; j < seats.size(); ++j) {
					diss[j] = min(diss[j], j - i);
				}
			}
		}
		int maxdis = -1;
		int ans = -1;
		for (int i = 0; i < seats.size(); ++i) {
			if (maxdis < diss[i]) {
				maxdis = diss[i];
				ans = i;
			}
		}
		seats[ans] = who;
		return;
	}
	assert(false);
}

int main() {
	while (1) {
		int N, M; cin >> N >> M;
		if (!N)break;
		vector<int>seats(N);
		for (int i = 0; i < M; ++i) {
			char c; cin >> c;
			int num = c - 'A' + 1;
			sit(seats, num); 
			for (int i = 0; i < N; ++i) {
				if (seats[i]) {
					cout << char('A' + seats[i] - 1);
				}
				else {
					cout << '#';
				}
			}
			cout << endl;
		}
	
	}
	return 0;
}

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;
			break;
		}
	}
	for(int i = k; i >= 1; --i){
		if(chair[i]){
			ret = std::min(ret, k - i);
			break;
		}
	}
	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;
}