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 <map>
#include <queue>
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();

		//d¡p^[Ícontinue
		if(d[p.first]) continue;

		string str = p.first;

		//SF¯¶©Ç¤©Ì`FbN
		bool flag = false;
		for(int i=0;i<str.size()-1;i++){
			if(str[i] != str[i+1]){
				flag = true;
				break;
			}
		}
		//¯¶Èçreturn
		if(!flag) return p.second;

		//d¡p^[»Êp
		d[p.first] = p.second;

		for(int i=0;i<str.size()-1;i++){
			//×èí¹ÅFªÙÈéÆ«
			if(str[i] != str[i+1]){
				char temp;
				string next;

				//tempÉÜÜêÈ¢êFðãü
				if(str[i] != 'b' && str[i+1] != 'b'){
					temp = 'b';
				}else if(str[i] != 'g' && str[i+1] != 'g'){
					temp = 'g';
				}else{
					temp = 'r';
				}

				//Ï»ãÌÔðnextÉlßÞ
				next = str;
				next[i] = next[i+1] = temp;

				//L[ÉvbV
				que.push(P(next, p.second+1));
			}
		}
	}
	return -1;
}

int main(){
	string worm;
	while(cin >> worm && worm != "0"){
		int ret = bfs(worm);
		if(ret>=0) cout << ret << endl;
		else cout << "NA" << endl;
	}
}

C++: #define _USE_MATH_DEFINES
#include <iostream>
#include <complex>
#include <algorithm>
#include <vector>
#include <stack>
#include <string>
#include <queue>
#include <cmath>
#include <math.h>
#include <numeric>
#include <list>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <climits>
#include <set>
#include <memory.h>
#include <memory>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cassert>
#include <map>
#include <cassert>
#include <time.h>
#include <ctime>

using namespace std;

typedef complex<double> xy_t;
typedef pair<xy_t, xy_t> line;
typedef long long ll;
typedef pair<int, int> P;
typedef pair<int , P> PP;
typedef pair<int, string> Ps;
typedef vector<int> vec;
typedef vector<vec> mat;
const int INF = 1 << 30;
const double EPS = 1e-9;
const double PI = 3.1415926535897932384626433832795;
const int CLK = CLOCKS_PER_SEC;

#define rep(i, n) for(int i = 0; i < n; i++)
#define rep2(i, m, n) for(int i = m; i < n; i++)


int memo[1 << 20];
int w[10];
int f[3];

void make_f(int n){
	rep(i, 3){
		int num = 0;
		rep(j, n){
			num = num * 4 + i;
		}
		f[i] = num;
	}
}

int get_s(const string &s){
	int res = 0;
	rep(i, s.size()){
		res *= 4;
		if(s[i] == 'r') res++;
		if(s[i] == 'g') res += 2;
	}
	return res;
}

int get_color(int a, int b){
	int c = min(a, b);
	int d = max(a, b);
	if(c == 0 && d == 1) return 2;
	if(c == 0 && d == 2) return 1;
	else return 0;
}

int get_num(int *w, int n){
	int res = 0;
	for(int i = 0; i < n; i++){
		res = res * 4 + w[i];
	}
	return res;
}

void to_w(int num, int n){
	for(int i = 0; i < n; i++){
		w[i] = num % 4;
		num /= 4;
	}
	reverse(w, w + n);
}

int main(){
	int n, start;
	string s;
	while(cin >> s && s != "0"){
		memset(memo, -1, sizeof(memo));
		n = s.size();
		start = get_s(s);
		make_f(n);
		queue<int> que;
		que.push(start);
		memo[start] = 0;
		bool ok = false;
		while(!que.empty()){
			int num = que.front();
			int c = memo[num];
			que.pop();
			if(num == f[0] || num == f[1] || num == f[2]){
				cout << c << endl;
				ok = true;
				break;
			}
			to_w(num, n);
			rep(i, n-1){
				if(w[i] != w[i+1]){
					int a = w[i];
					int b = w[i+1];
					w[i] = get_color(a, b);
					w[i+1] = get_color(a, b);
					int num2 = get_num(w, n);
					if(memo[num2] == -1){
						memo[num2] = c + 1;
						que.push(num2);
					}
					w[i] = a;
					w[i+1] = b;
				}
			}
		}
		if(!ok) cout << "NA" << endl;
	}
	return 0;
}