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 <queue>
#include <map>
#define INF 10000000
using namespace std;
typedef pair<string ,int>P;
int cnt;

int bfs(string worm){
  map<string,int>used;
  queue<P> que;
  que.push(P(worm,0));
  string next;
  
  while(!que.empty()){
    char tmp;
    P p = que.front();
    que.pop();
    if(used[p.first] == 1)continue;
    bool f = true;
    string str = p.first;
    for(int i = 0 ; i < p.first.size()-1 ; i++ ){
      if(str[i] != str[i+1])f = false;
    }
    if(f)return p.second;
    used[p.first] = 1;
    for(int i = 0 ; i < worm.size()-1 ; i++ ){
      if(str[i] != str[i+1]){
	if(str[i] != 'r' && str[i+1] != 'r'){
	  tmp = 'r';
	}else if(str[i] != 'g' && str[i+1] != 'g'){
	  tmp = 'g';
	} else {
	  tmp = 'b';
      }
	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;
    cnt = 0;
    int ret = bfs(worm);
    if(ret == -1){
      cout << "NA" << endl;
    }else cout << ret << endl;
    
  }
  return 0;
}

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

using namespace std;

typedef pair<string, int> P;

//????????????????????????????????????
bool judge(string str) {
	for (int i = 0; i < str.size(); ++i) {
		if (str[0] != str[i]) return false;
	}
	return true;
}

//??£?????????2?????????????????§?????????????????????
char color(char a, char b){
	if((a == 'g' && b == 'r') || (a == 'r' && b == 'g'))return 'b';
	else if((a == 'b' && b == 'r') || (a == 'r' && b == 'b')) return 'g';
	else if((a == 'g' && b == 'b') || (a == 'b' && b == 'g')) return 'r';
}

int solve(string s ){

	queue<P> q;
	map<string, int> m;
	q.push(P(s, 0));	//?????\??????????????¶????????\??????

	while (!q.empty()) {	//?????\??????????????¶?????????????????§
		P p = q.front();
		q.pop();
		if(m[p.first]) continue;	//??????????????????
		string now = p.first;
		if (judge(now)) return p.second;
		for (int i = 0; i < now.size() - 1; ++i) {
			if (now[i] != now[i+1]){	//??£?????????2????????°????????¨???
				char tmp = color(now[i], now[i + 1]);
				string D = now;
				D[i] = tmp;
				D[i + 1] = tmp;
				q.push(P(D, p.second + 1));
			}
		}
	}
	return -1;
}

int main() {
	string worm;
	while (cin >> worm) {
		if (worm == "0") break;
		int count = solve(worm);
		if (count == -1) cout << "NA" << endl;
		else cout << count << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<queue>
#include<map>
using namespace std;
queue<pair<string,int> >Q;
map<string,int> M;
int main()
{
	for(;;)
	{
		string s;
		cin>>s;
		if(s=="0")break;
		Q.push(make_pair(s,0));
		M[s]=1;
		int res=999;
		for(;!Q.empty();)
		{
			pair<string,int>p=Q.front();Q.pop();
			s=p.first;
			int flg=0;
			for(int i=0;i<s.length()-1;i++)
			{
				if(s[i]!=s[i+1])
				{
					flg=1;
					s[i]=s[i+1]=315-s[i]-s[i+1];
					if(M[s]==0)
					{
						M[s]=1;
						pair<string,int> ins(s,p.second+1);
						Q.push(ins);
					}
					s=p.first;
				}
			}
			if(flg==0)
				res=min(res,p.second);
		}
		if(res==999)cout<<"NA"<<endl;
		else cout<<res<<endl;
		M.clear();
	}
}