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 <set>
#include <string>
#include <queue>
using namespace std;


class Worm {
public:
	string str;
	int turn;
	Worm(string st, int t) : str(st), turn(t) {}
};

Worm nWorm(Worm w, int p) {
	if (w.str[p] > w.str[p+1]) {
		char t=w.str[p];
		w.str[p] = w.str[p+1];
		w.str[p+1] = t;
	}

	if (w.str[p]=='b' && w.str[p+1]=='g') w.str[p] = w.str[p+1] = 'r';
	else if (w.str[p]=='b' && w.str[p+1]=='r') w.str[p] = w.str[p+1] = 'g'; 
	else if (w.str[p]=='g' && w.str[p+1]=='r') w.str[p] = w.str[p+1] = 'b';

	w.turn++;
	return w;
}

int main() {
	string str;
	while (cin >> str, str[0]!='0') {
		queue<Worm> q;
		Worm init(str, 0);
		q.push(init);
		bool f=false, fl;
		set<string> s;
		s.insert(str);

		while (!q.empty()) {
			Worm tmp = q.front(); q.pop();
			for (int i=0; i<tmp.str.size()-1; i++) {
				Worm next = nWorm(tmp, i);
				if (s.insert(next.str).second) q.push(next);
			}

			fl = true;
			char c = tmp.str[0];
			for (int i=1; i<tmp.str.size(); i++)
				if (tmp.str[i] != c) { fl=false; break; }

			if (fl) { cout << tmp.turn << endl; f=true; break; }
		}

		if (!f) cout << "NA" << endl;
	}
	return 0;
}

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

typedef pair<string, int> psi;

int bfs(string worm) {
  queue<psi> que;
  que.push(psi(worm, 0));

  map<string, int> d;

  while (!que.empty()) {
    psi 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 temp;
	string next;

	if (str[i] != 'b' && str[i+1] != 'b') {
	  temp = 'b';
	} else if (str[i] != 'g' && str[i+1] != 'g') {
	  temp = 'g';
	} else {
	  temp = 'r';
	}

	next = str;
	next[i] = next[i+1] = temp;

	que.push(psi(next, p.second+1));
      }
    }
  }
  return -1;
}

int main(void) {
  string worm;
  while (cin >> worm) {
    if (worm[0] == '0') {
      break;
    }

    int ret = bfs(worm);
    if (ret != -1) {
      cout << ret << endl;
    } else {
      cout << "NA" << endl;
    }
  }

  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iostream>
#include <cctype>
#include <sstream>
#include <string>
#include <list>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <utility>
#include <numeric>
#include <algorithm>
#include <iterator>
#include <bitset>
#include <complex>
#include <fstream>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
template<class T> T RoundOff(T a){ return int(a+.5-(a<0)); }
template<class T, class C> void chmax(T& a, C b){ if(a < b) a = b; }
template<class T, class C> void chmin(T& a, C b){ if(b < a) a = b; }
template<class T, class C> pair<T, C> mp(T a, C b){ return make_pair(a, b); }

char derv(char c1, char c2)
{
	string res("rgb");
	
	res.erase(res.begin() + res.find(c1));
	res.erase(res.begin() + res.find(c2));
	
	return res[0];
}

string conv(string str, int p, char c)
{
	str[p + 0] = c;
	str[p + 1] = c;
	return str;
}

string answer[16][4];

void init()
{
	rep(i, 16)
	{
		answer[i][0] = string().append(i, 'r');
		answer[i][1] = string().append(i, 'g');
		answer[i][2] = string().append(i, 'b');
	}
}

inline bool check(const string& str)
{
	bool res = false;
	
	rep(i, 3) res |= str == answer[str.size()][i];
	
	return 	res;
}

template<class T>
string toString(T sig)
{
	stringstream ss;
	
	ss << sig;
	
	return ss.str();
}

int main()
{
	init();
	
    for(string worm; cin >> worm && worm != "0";)
	{
		int n = worm.size();
		string ans("NA");
		queue<pair<int, string> > que;
		map<string, int> table;
		
		
		for(que.push(mp(0, worm)); !que.empty(); que.pop())
		{
			string sub(que.front().second);
			int times = que.front().first;
			
			if(table[sub] != 0) continue;
			else table[sub] = 1;
			
			if(check(sub))
			{
				ans = toString(times);
				break;
			}
			
			rep(i, sub.size() - 1) if(sub[i] != sub[i + 1])
			{
				char d = derv(sub[i], sub[i + 1]);
				
				que.push(mp(times + 1, conv(sub, i, d)));
			}
		}
		
		cout << ans << endl;
	}
}