Go: package main

import (
    "bufio"
    "os"
    "fmt"
)

var sc = bufio.NewScanner(os.Stdin)

/**************  Cell  *****************/
type Cell struct {
    item interface{}
    next *Cell
    prev *Cell
}

func NewCell(x interface{}, ne *Cell, pr *Cell) *Cell {
    newCp := new(Cell)
    newCp.item = x
    newCp.next = ne
    newCp.prev = pr
    return newCp
}
/************  End Cell  ***************/

/**************  Queue  ****************/
type Queue struct {
    size int
    front *Cell
    rear *Cell
}

func NewQueue() *Queue {
    return new(Queue)
}

func (q *Queue) Push(x interface{}) {
    newNode := NewCell(x, nil, nil)
    if q.size == 0 {
        q.front = newNode
        q.rear = newNode
    } else {
        newNode.prev = q.rear
        q.rear.next = newNode
        q.rear = newNode
    }
    q.size++
}

func (q *Queue) PopLeft() interface{} {
    if q.size == 0 {
        return nil
    } else {
        x := q.front.item
        if q.size == 1 {
            q.front = nil
            q.rear = nil
        } else {
            q.front = q.front.next
            q.front.prev = nil
        }
        q.size--
        return x
    }
}

func (q *Queue) IsEmpty() bool {
    return q.size == 0
}

func (q *Queue) Length() int {
    return q.size
}

type State struct {
    color string
    cnt int
}

func main() {
    for {
        sc.Scan()
        init := sc.Text()
        if init == "0" {
            break
        }
        bfs(init)
    }
}

func bfs(init string) {
    dic := make(map[string]int)
    que := NewQueue()
    que.Push(State{init, 0})
    length := len(init)
    isSolved := false
    for !que.IsEmpty() {
        state := que.PopLeft().(State)
        _, ok := dic[state.color]
        if ok {
            continue
        } else {
            dic[state.color] = state.cnt
        }

        if isSingleColor(state.color) {
            fmt.Println(state.cnt)
            isSolved = true
            break
        }

        for i := 0;i < length - 1; i++ {
            color1, color2 := string(state.color[i]), string(state.color[i + 1])
            if color1 != color2 {
                color3 := other(color1, color2)
                if i <= length - 2 {
                    que.Push(State{state.color[:i] + color3 + state.color[i + 2:], state.cnt + 1})
                } else {
                    que.Push(State{state.color[:i] + color3, state.cnt + 1})
                }
            }
        }
    }
    if !isSolved {
        fmt.Println("NA")
    }
}

func other(color1, color2 string) string {
    if color1 == "r" {
        if color2 == "g" {
            return "bb"
        } else if color2 == "b" {
            return "gg"
        }
    } else if color1 == "g" {
        if color2 == "r" {
            return "bb"
        } else if color2 == "b" {
            return "rr"
        }
    } else if color1 == "b" {
        if color2 == "r" {
            return "gg"
        } else if color2 == "g" {
            return "rr"
        }
    }
    return ""
}

func isSingleColor(color string) bool {
    for _, c := range color {
        if string(c) != string(color[0]) {
            return false
        }
    }
    return true
}

C++: #include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;
int que[60000][10],flg[1050000];
int main(void){
	int p1,p2,i,j,len,time[60000],copy[10],f,x,ans,iro;
	char ca[11];
	while(1){
		cin>>ca;
		if(ca[0]=='0') break;
		len=strlen(ca);
		for(i=0;i<len;i++){
			if(ca[i]=='r') que[0][i]=0;
			if(ca[i]=='g') que[0][i]=1;
			if(ca[i]=='b') que[0][i]=2;
		}
		for(i=0;i<=1050000;i++) flg[i]=0;
		p1=0; p2=1; time[0]=0; ans=-1;
		while(1){
			if(p1==p2){
//				cout<<p1<<endl;
				break;
			}
		  /*cout<<p1<<' ';
			for(i=0;i<len;i++) cout<<que[p1][i];
			cout<<' '<<time[p1]<<endl;*/
			f=1;
			for(i=0;i<len-1;i++){
				if(que[p1][i]!=que[p1][i+1]){
					f=0;
					break;
				}
			}
			if(f==1){
				ans=time[p1];
				break;
			}
			for(i=0;i<len-1;i++){
				for(j=0;j<len;j++) copy[j]=que[p1][j];
				if(copy[i]!=copy[i+1]){
					iro=copy[i]+copy[i+1];
					if(iro==3){
						copy[i]=0; copy[i+1]=0;
					}
					if(iro==2){
						copy[i]=1; copy[i+1]=1;
					}
					if(iro==1){
						copy[i]=2; copy[i+1]=2;
					}
				}
				x=copy[0];
				for(j=1;j<len;j++) x=x*4+copy[j];
				if(flg[x]==0){
					flg[x]=1; time[p2]=time[p1]+1;
					for(j=0;j<len;j++) que[p2][j]=copy[j];
					p2++;
				}
			}
			p1++;
		}
		if(ans==-1) cout<<"NA"<<endl;
		else cout<<ans<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<map>
#include<set>
#include<utility>
#include<vector>
#include<cmath>
#include<cstring>
#include<cstdio>
#include<time.h>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mp make_pair
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
const double EPS=1e-10;
const int inf=1e8;
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
int main(){
	map<string,string>q;
	q["bg"]=q["gb"]="rr";
	q["gr"]=q["rg"]="bb";
	q["rb"]=q["br"]="gg";
	string s;
	while(cin>>s,s!="0"){
		vector<string>in;
		map<string,bool>tmp;
		in.pb(s);
		int co=0;
		while(1){
			vector<string>out;
			bool h;
			rep(i,in.size()){
				string s=in[i];
				tmp[s]=true;
				h=true;
				char qq=in[i][0];
				rep(j,s.size())if(qq!=in[i][j])h=false;
				if(h)break;
				rep(j,s.size()-1)if(s[j]!=s[j+1]){
					string www=s.substr(j,2);
					string w=q[www];
					string ww=s;
					ww[j]=w[0];ww[j+1]=w[1];
					if(tmp[ww]==false)out.pb(ww);
				}
			}
			if(h)break;
			co++;
			in=out;
			//cout<<" "<<in.size()<<endl;
			if(co==10)break;
		}
		if(co==11)cout<<"NA"<<endl;
		else cout<<co<<endl;
	}
}

C++: #include <iostream>
#include <queue>
#include <set>
using namespace std;

class Info{
public:
	string s;
	int depth;
};

bool is_answer(string s){
	for(int i=1;i<s.length();i++){
		if(s.at(0) != s.at(i)) return false;
	}
	return true;
}

string change_color(string s, int i){
	char f = s.at(i);
	char b = s.at(i+1);

	if(f == 'r' && b == 'g' || f == 'g' && b == 'r'){
		s.replace(i,2,"bb");
	}
	else if(f == 'r' && b == 'b' || f == 'b' && b == 'r'){
		s.replace(i,2,"gg");
	}
	else if(f == 'g' && b == 'b' || f == 'b' && b == 'g'){
		s.replace(i,2,"rr");
	}

	return s;
}

int bfs(string s){
	int len = s.length();
	set<string> worm_set;
	queue<Info> q;
	Info tmp = {s,0};

	if(is_answer(s)){
		return 0;
	}

	q.push(tmp);
	worm_set.insert(s);

	while(!q.empty()){
		tmp = q.front(); q.pop();

		for(int i=0;i<len-1;i++){
			string next_worm = change_color(tmp.s,i);

			if(is_answer(next_worm)){
				return tmp.depth + 1;
			}

			if(next_worm != tmp.s &&
				 worm_set.find(next_worm) == worm_set.end()){
				Info next_info = {next_worm, tmp.depth + 1};

				q.push(next_info);
				worm_set.insert(next_worm);
			}
		}
	}

	return -1;
}

int main(void){
	string s;

	while(cin >> s && s != "0"){
		int ans = bfs(s);

		if(ans >= 0){
			cout << ans << endl;
		}
		else{
			cout << "NA\n";
		}
	}

  return 0;
}