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 <queue>
#include <algorithm>

using namespace std;

typedef pair <string, int> P;

#define mp(a, b) make_pair(a, b)

char diff(char a, char b)
{
	if (a != 'r' && b != 'r') return 'r';
	if (a != 'g' && b != 'g') return 'g';
	if (a != 'b' && b != 'b') return 'b';
	return 'a';
}

bool check(string str)
{
	char c = str[0];
	for (int i = 0; i < str.length(); i++){
		if (c != str[i]) return false;
	}

	return true;
}

int main(void)
{
	string str;

	while (cin >> str){
		if (str == "0") return 0;

		int ret = -1, a;
		queue < P > q;
		q.push(mp(str, 0));
		while (!q.empty()){
			P now = q.front();
			q.pop();
			if (check(now.first)){
				ret = now.second;
				break;
			}
			if (q.size() > 700000){
				break;
			}
			for (int i = 0; i < now.first.length()-1; i++){
				if (now.first[i] != now.first[i + 1]){
					string tmp = now.first;
					tmp[i] = diff(now.first[i], now.first[i + 1]);
					tmp[i + 1] = diff(now.first[i], now.first[i + 1]);
					q.push(mp(tmp, now.second + 1));
				}
			}
		}

		if (ret >= 0) cout << ret << endl;
		else cout << "NA" << endl;
	}

	return 0;
}

C++: #include <iostream>
#include <string>
#include <queue>
#include <vector>
#include <set>

using namespace std;

typedef vector<int> vi;
auto ok = [](const vi & v){
    for (int i = 1; i < v.size(); i++){
        if (v[i] != v[0]) return false;
    }
    return true;
};

struct state {
    vi v;
    int n;
};

namespace std{
    ostream & operator<<(ostream & os, const vi & v){
        os << '(';
        for (int i = 0; i < v.size(); i++){
            cout << v[i] << ',';
        }
        os << ')';
        return os;
    }
}

int main(){
    string s;
    while (cin >> s, s!="0"){
        vi init(s.size());
        for (int i = 0; i < s.size(); i++){
            if (s[i] == 'r') init[i] = 0;
            else if (s[i] == 'g') init[i] = 1;
            else init[i] = 2;
        }
        queue<state> q;
        set<vi> dp;
        q.push({ init, 0 });

        int ans = -1;
        while (q.size()){
            state sta = q.front();
            q.pop();
            vi & sv = sta.v;
            //cout << sv << endl;
            auto pr = dp.insert(sv);
            if (!pr.second){
                continue;
            }
            if (ok(sv)){
                ans = sta.n;
                break;
            }
            for (int i = 1; i < sv.size(); i++){
                if (sv[i] != sv[i - 1]){
                    int a = sv[i];
                    int b = sv[i - 1];
                    sv[i] = sv[i - 1] = 3 - (a + b);
                    q.push({ sv, sta.n + 1 });
                    sv[i] = a;
                    sv[i - 1] = b;
                }
            }
        }
        if (ans == -1){
            cout << "NA" << endl;
        }
        else{
            cout << ans << endl;
        }
    }
}

C++: #include<iostream>
#include<string>
#include<queue>
#include<map>
using namespace std;
int main(){

  string s,str,col[3];
  queue<string> que;
  map<string,int> mp;
  int flag;
  while(cin >> s,s != "0"){
    mp.clear();
    flag = 1;
    que.push(s);
    mp[s] = 0;
    for(int i=0;i<3;i++) col[i] = "";
    for(int i=0;i<s.size();i++){
      col[0] += "r";
      col[1] += "b";
      col[2] += "g";
    }
    while(!que.empty()){
      if(que.front()==col[0]){
	cout << mp[col[0]] << endl;
	flag--;
	break;
      }
      if(que.front()==col[1]){
	cout << mp[col[1]] << endl;
	flag--;
	break;
      }
      if(que.front()==col[2]){
	cout << mp[col[2]] << endl;
	flag--;
	break;
      }
      
      for(int i=0;i<s.size()-1;i++){
	str = que.front();
	if(str[i] != str[i+1]){
	  if(str[i] != 'r' && str[i+1] != 'r'){
	    str[i] = 'r';
	    str[i+1] = 'r';
	  } else if(str[i] != 'b' && str[i+1] != 'b'){
	    str[i] = 'b';
	    str[i+1] = 'b';
	  }else if(str[i] != 'g' && str[i+1] != 'g'){
	    str[i] = 'g';
	    str[i+1] = 'g';
	  }
	  if(mp.count(str) == 0){
	    que.push(str);
	    mp[str] = mp[que.front()]+1;
	  }
	}
      }
      que.pop();
    }
    while(!que.empty()) que.pop();
    if(flag) cout << "NA" << endl;
  }
  return (0);
}