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 <bits/stdc++.h>

#define FOR(i, n, m) for(int i = (n);i < (m);i++)
#define REP(i, n) for(int i = 0;i < (n);i++)
#define PII pair<int, int>

using namespace std;

string worm;

int all(string a){
    char b = a[0];
    int cnt = 0;
    for(int i = 1;a[i] != '\0';i++){
        if(a[i] != b)
            cnt++;
    }
    return cnt;
}

int solve(){
    queue< pair<string, int> > que;
    que.push(pair<string, int>(worm, 0));

    if(all(worm) == 0){
        return 0;
    }

    while(que.size()){
        string worm1 = que.front().first;
        int num = que.front().second;
        que.pop();

        if(all(worm1) == 1){
            continue;
        }else if(all(worm1) == 0){
            return num;
        }

        if(num > 100){
            return -1;
        }

        for(int i = 0;i < strlen(worm1.c_str())-1;i++){
            string tmp = worm1;
            if(worm1[i] != worm1[i+1]){
                if((worm1[i] == 'b' && worm1[i+1] == 'g') || (worm1[i] == 'g' && worm1[i+1] == 'b')){
                    tmp[i] = tmp[i+1] = 'r';
                    que.push(pair<string, int>(tmp, num+1));
                }else if((worm1[i] == 'b' && worm1[i+1] == 'r') || (worm1[i] == 'r' && worm1[i+1] == 'b')){
                    tmp[i] = tmp[i+1] = 'g';
                    que.push(pair<string, int>(tmp, num+1));
                }else{
                    tmp[i] = tmp[i+1] = 'b';
                    que.push(pair<string, int> (tmp, num+1));
                }
            }
        }
    }

    return -1;
}

int main(void){
    cin >> worm;
    while(worm[0] != '0'){
        int result = solve();
        if(result >= 0){
            cout << result << endl;
        }else{
            cout << "NA" << endl;
        }
        cin >> worm;
    }

    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <complex>
#include <cstring>
#include <cstdlib>
#include <string>
#include <cmath>
#include <queue>
#include <map>
using namespace std;

#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
const int INF = 1<<30;

char hage[] = {'r','g','b'};
char hoge(char a, char b) {
  REP(i,3)
    if (a != hage[i] && b != hage[i])
      return hage[i];
}
typedef pair<int, string> pis;

int bfs(string s) {
  int res = INF;
  queue<pis> Q;
  map<string, bool> ma;
  Q.push(pis(0,s));
  while(!Q.empty()) {
    pis p = Q.front(); Q.pop();
    string ss = p.second;
    if (ma[ss]) continue;
    ma[ss] = true;
//    cout << p.first << " " <<ss << endl;
    bool f = true;
    REP(i, ss.length()-1)
      if (ss[i] != ss[i+1])
        f = false;
    if (f) return p.first;
    REP(i, ss.length()-1) {
      if (ss[i] != ss[i+1]) {
        string sss = ss;
        sss[i] = sss[i+1] = hoge(ss[i], ss[i+1]);
        Q.push(pis(p.first + 1, sss));
      }
    }
  }
  return -1;
}

int main() {
  string s;
  while(cin >> s, s != "0") {
    int ans = bfs(s);
    if (ans >= 0)
      cout << ans << endl;
    else
      cout << "NA" << endl;
  }
}

C++: #include <bits/stdc++.h>

using namespace std;

#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define Rrep(i, j) for(int i = j; i >= 0; --i)
#define INF (1 << 30)

typedef long long ll;
typedef unsigned long long ull;
typedef pair<string, int> P;

string warm;

/*???????????????????????????*/
bool SameCol(string col) {
	rep(i, col.size() - 1) {
		if(col[i] != col[i + 1]) return false;
	}
	return true;
}
/*????????????*/
char ChangeCol(char a, char b) {
	if((a == 'r' && b == 'b') || (a == 'b' && b == 'r')) return 'g';
	else if((a == 'r' && b == 'g') || (a == 'g' && b == 'r')) return 'b';
	else if((a == 'b' && b == 'g') || (a == 'g' && b == 'b')) return 'r';
}

int solve(string s) {
	map<string, bool> m;	/*???????????\??¨*/
	queue<P> q;
	q.push(P(s, 0));

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

		/*????????????*/
		if(m[p.first]) continue;
		m[p.first] = true;

		if(SameCol(p.first)) return p.second;
		string now = p.first;
		rep(i, now.size() - 1) {
			if(now[i] != now[i + 1]) {
				char tmp = ChangeCol(now[i], now[i + 1]);
				string tmp2 = now;
				tmp2[i] = tmp; tmp2[i + 1] = tmp;
				q.push(P(tmp2, p.second + 1));
			}
		}
	}
	return -1;
}

int main() {
	while(cin >> warm) {
		if(warm == "0") break;
		int ans = solve(warm);
		if(ans == -1) printf("NA\n");
		else printf("%d\n", ans);
	}
	return 0;
}