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 <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	int n, m;
	char str[10001];
	
	while (scanf("%d %d", &n, &m) && n){
		memset(str, '#', sizeof(str));
		vector<int> used;
		str[n] = 0;
		for (int i = 0; i < m; i++){
			char p;
			scanf(" %c", &p);
			
			if (p == 'A'){
				for (int pos = 0; pos < n; pos++){
					if (str[pos] == '#'){
						str[pos] = 'A';
						used.push_back(pos);
						break;
					}
				}
			}
			if (p == 'B'){
				bool seated = false;
				for (int pos = n - 1; pos; pos--){
					if (str[pos] == '#' && (pos == 0 || str[pos - 1] != 'A')){
						str[pos] = 'B';
						used.push_back(pos);
						seated = true; break;
					}
				}
				if (!seated)
					for (int pos = 0; pos < n; pos++){
					if (str[pos] == '#'){
						str[pos] = 'B'; used.push_back(pos);
						break;
					}
				}
			}
			if (p == 'C'){
				if (i == 0){
					if (n & 1){
						str[(n + 1) / 2 - 1] = 'C';
						used.push_back((n + 1) / 2 - 1);
					}
					else {
						str[n / 2] = 'C';
						used.push_back(n / 2);
					}
				}
				else {
					for (int pos = 0; pos < n; pos++){
						if (str[pos] != '#'){
							if (pos + 1 < n && str[pos + 1] == '#'){
								str[pos + 1] = 'C';
								used.push_back(pos + 1);
								break;
							}
							if (pos - 1 >= 0 && str[pos - 1] == '#'){
								str[pos - 1] = 'C';
								used.push_back(pos - 1);
								break;
							}
						}
					}
				}
			}
			if (p == 'D'){
				if (i == 0){
					str[0] = 'D';
					used.push_back(0);
				}
				else {
					sort(used.begin(), used.end());
					int maxDist = -1, maxPos = -1;
					for (int pos = 0; pos < n; pos++){
						if (str[pos] == '#'){
							int a = upper_bound(used.begin(), used.end(), pos) - used.begin() - 1;
							int b = upper_bound(used.begin(), used.end(), pos) - used.begin();
							int tDist = 999999;
							if (a != -1) tDist = min(tDist, pos - used[a]);
							if (b != used.size()) tDist = min(tDist, used[b] - pos);
							if (tDist > maxDist){
								maxDist = tDist;
								maxPos = pos;
							}
						}
					}
					str[maxPos] = 'D';
					used.push_back(maxPos);
				}
			}
			if (0) printf("%s\n", str);
		}
		printf("%s\n", str);
	}
}

C++: /*
 * src.cpp
 *
 *  Created on: 2016/07/27
 *      Author: joi
 */

#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,a) FOR(i,0,a)

using namespace std;

const int MAX_N=1e2,INF=1e8;

int n,m;

char chairs[MAX_N+1];

int dist(int a){
	int res=INF;
	REP(i,n){
		if (chairs[i]!='#'){
			res=min(res,abs(i-a));
		}
	}
	return res;
}

int main(){
	do{
		cin>>n>>m;
		if (n || m){
			cin.ignore();
			REP(i,n){
				chairs[i]='#';
			}
			chairs[n]=0;
			REP(i,m){
				char c;
				cin>>c;
				switch (c){
				case 'A':{
					REP(i,n){
						if (chairs[i]=='#'){
							chairs[i]='A';
							break;
						}
					}
					break;
				}
				case 'B':{
					int v=-1;
					for (int i=n-1;i>=0;i--){
						if (chairs[i]=='#'){
							if (i!=0){
								if (chairs[i-1]=='A'){
									continue;
								}
							}
							if (i+1!=n){
								if (chairs[i+1]=='A'){
									continue;
								}
							}
							v=i;
							break;
						}
					}
					if (v!=-1){
						chairs[v]='B';
					}else{
						REP(i,n){
							if (chairs[i]=='#'){
								chairs[i]='B';
								break;
							}
						}
					}
					break;
				}
				case 'C':{
					if (i==0){
						if (n%2==1){
							chairs[(n+1)/2-1]='C';
						}else{
							chairs[n/2]='C';
						}
					}else{
						REP(i,n){
							if (chairs[i]!='#'){
								if (i+1!=n && chairs[i+1]=='#'){
									chairs[i+1]='C';
									break;
								}
								if (i!=0 && chairs[i-1]=='#'){
									chairs[i-1]='C';
									break;
								}
							}
						}
					}
					break;
				}
				case 'D':{
					int a=0,d=dist(0);
					FOR(i,1,n){
						if (dist(i)>d){
							a=i;
							d=dist(i);
						}
					}
					chairs[a]='D';
					break;
				}
				}
			}
			cout<<chairs<<endl;
		}
	}while(n || m);
	return 0;
}

C++: #include<iostream>
#include<queue>
#include<vector>
#include<utility>
#include<algorithm>

using namespace std;

#define REP(i,n); for(int i=0;i<(n);i++)

int vec1[]={0,1,-1,1,-1,0};
int vec2[]={1,1,0,0,-1,-1};

int t,n;
int table[200][200];

typedef pair<int,int> pii;
typedef pair<int,pii> piii;
queue<piii> q1;

int ans;

int solve(int y,int x){
	queue<piii> p;
	q1.push(make_pair(0,make_pair(y,x)));
	while(!q1.empty()){
		if(t <= q1.front().first)
			return 0;
		REP(i,6){
			int n_y = q1.front().second.first + vec1[i];
			int n_x = q1.front().second.second + vec2[i];
			if(table[n_y][n_x] = 0){
				ans++;
				table[n_y][n_x] = 1;
				q1.push(make_pair(q1.front().first + 1,make_pair(n_y,n_x)));
			}
		}
		q1.pop();
	}
	return 0;
}


int main(){
	while(cin>>t>>n,t+n){
		ans = 0;
		fill_n(table[0],200*200,0)
		REP(i,n){
			int x,y;
			cin>>x>>y;
			table[100+y][100+x] = 1;
		}
		int x,y;
		cin>>x>>y;
		table[100+y][100+x] = 1;
		solve(100+y,100+x);
		cout<<ans+1<<endl;
	}
	return 0;
}