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
			}
		}
		for i := 0; i < n; i++ {
			if i == n-1 {
				fmt.Println(chair[i])
			} else {
				fmt.Printf("%s ", chair[i])
			}
		}
	}
}

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>
using namespace std;
int main(){
long n,m,i,j,d[101],e[101],k,dd;
char c,a[101];
while(cin>>n){
cin>>m;
if(n==0)break;
for(i=0;i<n;i++)a[i]='#';
for(j=0;j<m;j++){
cin>>c;
if(c=='A'){
for(i=0;i<n;i++)if(a[i]=='#'){a[i]='A';break;}
}else if(c=='B'){
for(i=n-1;i>=0;i--){
if(a[i]!='#'||0<i&&a[i-1]=='A'||i<n-1&&a[i+1]=='A')continue;
a[i]='B';break;
}
if(i<0){for(i=0;i<n;i++)if(a[i]=='#'){a[i]='B';break;}}
}else if(c=='C'){
for(i=0;i<n;i++){
if(a[i]!='#'||0<i&&a[i-1]=='#'||i<n-1&&a[i+1]=='#')continue;
a[i]='C';break;
}
if(i==n)a[n/2]='C';
}else if(c=='D'){
for(i=0;i<n;i++)d[i]=-1;
for(i=0;i<n;i++)if(a[i]!='#')break;
if(i==n){a[0]='D';continue;}
for(;i<n;i++)if(a[i]=='#')d[i]=d[i-1]+1;else d[i]=0;
for(i=0;i<n;i++)e[i]=-1;
for(i=n-1;i>=0;i--)if(a[i]!='#')break;
for(;i>=0;i--)if(a[i]=='#')e[i]=e[i+1]+1;else e[i]=0;
for(i=0;i<n;i++)if(d[i]<e[i])d[i]=e[i];
dd=d[n-1];
for(i=n-1;i>=0;i--)if(dd<=d[i]){dd=d[i];k=i;}
a[k]='D';
}
}
a[n]=0;cout<<a<<endl;
}
return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <sstream>
#include <climits>
#include <cfloat>
#include <complex>

using namespace std;

int main()
{
	int n, m;
	while (scanf("%d %d", &n, &m), n | m)
	{
		char t[102];	// 1~n
		memset(t, '#', sizeof(t));
		for (int w = 0; w < m; ++w)
		{
			char c;
			scanf(" %c", &c);
			if (c == 'A')
			{
				int i;
				for (i = 1; t[i] != '#'; ++i)
					;
				t[i] = 'A';
			}
			else if (c == 'B')
			{
				int i;
				for (i = n; i >= 1; --i)
					if (t[i-1] != 'A' && t[i] == '#' && t[i+1] != 'A')
						break;
				if (i == 0)
					for (i = 1; t[i] != '#'; ++i)
						;
				t[i] = 'B';
			}
			else if (c == 'C')
			{
				int i;
				if (w == 0)
					i = n / 2 + 1;
				else
				{
					for (i = 1; ; ++i)
						if (t[i] != '#')
							if (t[i+1] == '#')
							{
								++i;
								break;
							}
							else if (t[i-1] == '#' && i > 1)
							{
								--i;
								break;
							}
				}
				t[i] = 'C';
			}
			else
			{
				int i;
				if (w == 0)
					i = 1;
				else
				{
					int dis[102];
					for (int j = 0; j < 102; ++j)
						dis[j] = 100000000;
					for (int j = 1; j <= n; ++j)
					{
						if (t[j] != '#')
							for (int k = 1; k <= n; ++k)
								dis[k] = min(dis[k], abs(j-k));
					}
					int d = 0;
					for (int j = 1; j <= n; ++j)
					{
						if (dis[j] > d)
						{
							i = j;
							d = dis[j];
						}
					}
				}
				t[i] = 'D';
			}
			printf("%c: ", c);
			for (int i = 1; i <= n; ++i)
				putchar(t[i]);
			printf("\n");
		}
		for (int i = 1; i <= n; ++i)
			putchar(t[i]);
		printf("\n");
	}

	return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <sstream>
#include <climits>
#include <cfloat>
#include <complex>

using namespace std;

int main()
{
	int n, m;
	while (scanf("%d %d", &n, &m), n | m)
	{
		char t[102];	// 1~n
		memset(t, '#', sizeof(t));
		for (int w = 0; w < m; ++w)
		{
			char c;
			scanf(" %c", &c);
			if (c == 'A')
			{
				int i;
				for (i = 1; t[i] != '#'; ++i)
					;
				t[i] = 'A';
			}
			else if (c == 'B')
			{
				int i;
				for (i = n; i >= 1; --i)
					if (t[i-1] != 'A' && t[i] == '#' && t[i+1] != 'A')
						break;
				if (i == 0)
					for (i = 1; t[i] != '#'; ++i)
						;
				t[i] = 'B';
			}
			else if (c == 'C')
			{
				int i;
				if (w == 0)
					i = n / 2 + 1;
				else
				{
					for (i = 2; ; ++i)
						if (t[i] != '#')
							if (t[i+1] == '#')
							{
								++i;
								break;
							}
							else if (t[i-1] == '#')
							{
								--i;
								break;
							}
				}
				t[i] = 'C';
			}
			else
			{
				int i;
				if (w == 0)
					i = 1;
				else
				{
					int dis[102];
					for (int j = 0; j < 102; ++j)
						dis[j] = 100000000;
					for (int j = 1; j <= n; ++j)
					{
						if (t[j] != '#')
							for (int k = 1; k <= n; ++k)
								dis[k] = min(dis[k], abs(j-k));
					}
					int d = 0;
					for (int j = 1; j <= n; ++j)
					{
						if (dis[j] > d)
						{
							i = j;
							d = dis[j];
						}
					}
				}
				t[i] = 'D';
			}
			printf("%c: ", c);
			for (int i = 1; i <= n; ++i)
				putchar(t[i]);
			printf("\n");
		}
		for (int i = 1; i <= n; ++i)
			putchar(t[i]);
		printf("\n");
	}

	return 0;
}