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<bits/stdc++.h>
using namespace std;
typedef long long int lld;
#define INF 100000
int main(){
  int n,m;
  while(cin >> n >> m , n || m){
    string str = "";
    for(int i=0;i<n;i++) str += '#';
    for(int c=0;c<m;c++){
      char h; cin >> h;
      if(h == 'A'){
	for(int i=0;i<n;i++){
	  if(str[i] == '#'){
	    str[i] = h;
	    break;
	  }
	}
      } else if(h == 'B'){
	int first = -1;
	bool flg = true;
	for(int i=n-1;i>=0;i--){
	  if(first == -1 && str[i] == '#') first = i;
	  if(str[i] == '#' && str[i-1] != 'A' && str[i+1] != 'A'){
	    str[i] = h;
	    flg = false;
	    break;
	  }
	  if(flg){
	    for(int i=0;i<n;i++){
	      if(str[i] == '#'){
		str[i] = h;
		break;
	      }
	    }	
	  }
	}
      } else if(h == 'C'){
	if(c == 0) str[(n%2==1 ? (n+1)/2 : (n/2+1)) -1] = 'C';
	else {
	  for(int i=0;i<n;i++){
	    if(str[i] != '#'){
	      if(str[i+1] == '#') {
		str[i+1] = h;
		break;
	      }
	      if(str[i-1] == '#') {
		str[i-1] = h;
		break;
	      }
	    }
	  }
	}
      } else {
	int first = -1;
	int k = (c==0 ? 0 : 1);
	int MAX=0,j,m,MAXi;
	for(int i=0;i<n;i++){
	  if(str[i]=='#'){
	    for(j=i-1;j>=0;j--) if(str[j]!='#') break;
	    for(m=i+1;m<n;m++) if(str[m]!='#') break;
	    if(j==-1) j = INF;
	    if(m==n) m = INF;
	    if(j==INF){
	      if(k-i > MAX) MAX = m-i,MAXi=i,MAXi=i;
	    } else if(m==INF){
	      if(i-j > MAX) MAX = i-j,MAXi=i;
	    } else{
	      if(min(m-i,i-j) > MAX) MAX=min(m-i,i-j),MAXi=i;
	    }
	  }
	}
	if(MAX == 0) {
	  for(int i=0;i<n;i++){
	    if(str[i] == '#'){
	      str[i] = h;
	      break;
	    }
	  }
	}
	else str[MAXi] = h;
      }
    }
    cout << str << endl;
  }
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <string>

#define int long long

using namespace std;

class Solver {
};

signed main() {
	while (true) {
		int n, m;
		cin >> n >> m;
		if (n == 0)break;

		vector<char> status(n, '#');
		for (int i = 0; i < m; i++) {
			char who;
			cin >> who;
			if (who == 'A') {
				for (int i = 0; i < n; i++) {
					if (status[i] == '#') {
						status[i] = 'A';
						break;
					}
				}
			}
			if (who == 'B') {
				bool valid = false;
				for (int i = n - 1; i >= 0; i--) {
					if (status[i] != '#')continue;

					if ((i + 1 < n && status[i + 1] == 'A')
						|| (i - 1 >= 0 && status[i - 1] == 'A'))continue;

					status[i] = 'B';
					valid = true;
					break;
				}

				if (!valid) {
					for (int i = 0; i < n; i++) {
						if (status[i] == '#') {
							status[i] = 'B';
							break;
						}
					}
				}
			}
			if (who == 'C') {
				bool valid = false;
				for (int i = 0; i <n; i++) {
					if (status[i] == '#')continue;

					if (i + 1 < n && status[i + 1] == '#') {
						status[i + 1] = 'C';
						valid = true;
						break;
					}
					if (i - 1 >= 0 && status[i - 1] == '#') {
						status[i - 1] = 'C';
						valid = true;
						break;
					}
				}

				if (!valid) {
					status[n / 2] = 'C';
				}
			}
			if (who == 'D') {
				vector<int> left(n, 0);
				int last = -1;
				for (int i = 0; i < n; i++) {
					if (status[i] != '#') last = i;
					else {
						if (last >= 0) left[i] = i - last;
						else left[i] = 1e9;
					}
				}
				last = -1;
				vector<int> right(n, 0);
				for (int i = n - 1; i >= 0; i--) {
					if (status[i] != '#')last = i;
					else {
						if (last >= 0) right[i] = last - i;
						else right[i] = 1e9;
					}
				}
				int now = 0;
				int dist = -1;
				for (int i = 0; i < n; i++) {
					if (status[i] != '#')continue;

					if (min(left[i], right[i]) > dist) {
						now = i;
						dist = min(left[i], right[i]);
					}
				}
				status[now] = 'D';
			}
		}

		for (int i = 0; i < n; i++) {
			cout << status[i];
		}
		cout << endl;
	}
}