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 <iostream>
#include <string>
#include <set>
#include <queue>
#include <map>

using namespace std;

int ans;
const int MAX_COUNT = 1000;
char color[3] = {'r', 'g', 'b'};
set<string> mSet;

typedef pair<string, int> PSI;

bool solve(string str)
{
	queue<PSI> que;
	que.push(PSI(str, 0));
	
	while(!que.empty())
	{
		PSI current = que.front();
		que.pop();

		bool is_solved = true;
		for(int i=0; i<current.first.size()-1; i++)
		{
			if(current.first[i] != current.first[i+1])
			{
				is_solved = false;
				break;
			}
		}

		if(is_solved)
		{
			ans = current.second;
			return true;
		}

		if(mSet.find(current.first) == mSet.end())
		{
			mSet.insert(current.first);
		}
		else
		{
			continue;
		}

 		for(int i=0; i<current.first.size()-1; i++)
		{
			if(current.first[i] != current.first[i+1])
			{
				for(int k=0; k<3; k++)
		   		{
	   				if(current.first[i] != color[k] && current.first[i+1] != color[k])
   					{
				   		string new_str = string(current.first.begin(), current.first.end());
			   			new_str[i] = color[k];
		  				new_str[i+1] = color[k];
						que.push(PSI(new_str, current.second+1));
					}
				}
			}
		}
	}

	return false;
}

int main()
{
	string str;
	while( 1 )
	{
		cin >> str;
		if(str == "0") break;

		ans = MAX_COUNT;
		mSet.clear();

		if(!solve(str))
		{
			printf("NA\n");
		}
		else
		{
			printf("%d\n", ans);
		}
	}
}

C++: #include <iostream>
#include <queue>
#include <map>
using namespace std;
typedef pair<string,int>P;
int bfs(string worm){
  queue<P>que;
  que.push(P(worm,0));
  map<string,int>d;
  while(!que.empty()){
    P p = que.front();
    que.pop();

    if(d[p.first])continue;
    string str = p.first;
    bool flag = false;
    for(int i = 0 ; i < str.size()-1 ; i++ ){
      if(str[i] != str[i+1] ){
	flag = true;
	break;
      }
    }
    if(!flag)return p.second;
    d[p.first] = p.second;
    for(int i = 0 ; i < str.size()-1 ; i++ ){
      if(str[i] != str[i+1]){
	char tmp;
	string next;
	if(str[i] != 'b' && str[i+1] != 'b'){
	  tmp = 'b'; 
	}else if(str[i] != 'g' && str[i+1] != 'g'){
	  tmp = 'g';
	}else {
	  tmp = 'r';
	}
	next = str;
	next[i] = next[i+1] = tmp;
	que.push(P(next,p.second + 1));
      }
    }
  }
  return -1;
}

int main(){
  string worm; 
  while(  cin >> worm ){
    if(worm[0] == '0' )break;  
    int ret = bfs(worm);
    if(ret >= 0)cout << ret << endl;
    else cout << "NA" << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <vector>
#include <utility>
#include <functional>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <deque>
#include <ctime>

using namespace std;

#define rep(i,n) REP(i,0,n)
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define pb push_back
//#define mp make_pair
#define all(r) (r).begin(),(r).end()
#define rall(r) (r).rbegin(),(r).rend()
#define fi first
#define se second

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int INF = 1e9;
const ll LINF = 1e18;
const ll MOD = 1e9 + 7;
double EPS = 1e-8;
const double PI = acos(-1);

int dx[]={-1,1,0,0};
int dy[]={0,0,-1,1};
string str;
string t;
string tmp;
int count;

int main(){
	while(cin >> str){
		map<string,int> mp;
		mp[str] = 0;
		if(str == "0"){
			break;
		}
		queue<string> q;
		q.push(str);

		char a[5] = {'r','g','b'};
		bool q_flag = true;

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

			for(int i=0; i+1<tmp.size(); i++){
				if(tmp[i] != tmp[i+1]){
					flag = false;
					for(int j=0; j<3; j++){
						if(a[j] != tmp[i] && a[j] != tmp[i+1]){
							t = tmp;
							t[i+1] = a[j];
							t[i] = a[j];
							if(mp.count(t) == 1){
								continue;
							}
							mp[t] = mp[tmp] + 1;
							q.push(t);
						}
					}
				}
			}
			if(flag == true){
				cout << mp[tmp] << endl;
				q_flag = false;
				break;
			}
		}

		if(q_flag == true){
			cout << "NA" << endl;
		}

	}

}