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 <set>
#include <queue>
#include <map>

using namespace std;

int ans;
const int MAX_COUNT = 1000;
char color[3] = {'r', 'g', 'b'};
set<string> mSet;

typedef pair<string, int> PSI;

bool solve(string str)
{
	queue<PSI> que;
	que.push(PSI(str, 0));
	
	while(!que.empty())
	{
		PSI current = que.front();
		que.pop();

		bool is_solved = true;
		for(int i=0; i<current.first.size()-1; i++)
		{
			if(current.first[i] != current.first[i+1])
			{
				is_solved = false;
				break;
			}
		}

		if(is_solved)
		{
			ans = current.second;
			return true;
		}

		if(mSet.find(current.first) == mSet.end())
		{
			mSet.insert(current.first);
		}
		else
		{
			continue;
		}

 		for(int i=0; i<current.first.size()-1; i++)
		{
			if(current.first[i] != current.first[i+1])
			{
				for(int k=0; k<3; k++)
		   		{
	   				if(current.first[i] != color[k] && current.first[i+1] != color[k])
   					{
				   		string new_str = string(current.first.begin(), current.first.end());
			   			new_str[i] = color[k];
		  				new_str[i+1] = color[k];
						que.push(PSI(new_str, current.second+1));
					}
				}
			}
		}
	}

	return false;
}

int main()
{
	string str;
	while( 1 )
	{
		cin >> str;
		if(str == "0") break;

		ans = MAX_COUNT;
		mSet.clear();

		if(!solve(str))
		{
			printf("NA\n");
		}
		else
		{
			printf("%d\n", ans);
		}
	}
}

C++: #include<cstdio>
#include<iostream>
#include<algorithm>
#include<queue>
#include<cmath>
using namespace std;
struct s{
    string worm;
    int nowans;
};
int main(){
    char dc[6][3]={'r','g','b','g','r','b','r','b','g','b','r','g','g','b','r','b','g','r'};
    while(1){
        int che[100000]={0},chenum=0;
        s IN,now;
        queue 
 que;
        cin >> IN.worm;
        IN.nowans=0;
        if(IN.worm[0]=='0')
            break;
        que.push(IN);
        while(1){
            chenum=0;
            now=que.front(),que.pop();
            for(int i=0;i<10;i++){
                if(now.worm[i]=='r')
                    chenum+=pow(3,i);
                else if(now.worm[i]=='g')
                    chenum+=pow(3,i)*2;
                else if(now.worm[i]=='b')
                    chenum+=pow(3,i)*3;
            }
            if(che[chenum])
                continue;
            else
                che[chenum]=1;
            for(int i=0;i<now.worm.size()-1;i++){
                if(now.worm[i]!=now.worm[i+1])
                    break;
                if(i==now.worm.size()-1-1){
                    printf("%d\n",now.nowans);
                    goto exit;
                }
            }
            if(now.nowans==20){
                puts("NA");
                goto exit;
            }
            for(int i=0;i<now.worm.size()-1;i++){
                if(now.worm[i]!=now.worm[i+1]){
                    for(int j=0;j<6;j++){
                        if(now.worm[i]==dc[j][0]&&now.worm[i+1]==dc[j][1]){
                            now.worm[i]=dc[j][2],now.worm[i+1]=dc[j][2],now.nowans++;
                            que.push(now);
                            now.worm[i]=dc[j][0],now.worm[i+1]=dc[j][1],now.nowans--;
                        }
                    }
                }
            }
        }
exit:
    printf("");
    }
    return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<string>
using namespace std;
bool same(char* seq){
  for(int i = 0; seq[i+1] != '\0'; ++i){
    if(seq[i] != seq[i+1]){
      return false;
    }
  }
  return true;
}
int dls(char* seq, int depth){
  if(depth<0){
    return false;
  }
  if(same(seq)){
    return true;
  }
  for(int i = 0; seq[i+1] != '\0'; ++i){
    char t = seq[i];
    char n = seq[i+1];
    if(t != n){
      if((t + n) == ('r' + 'b')){
        seq[i] = seq[i+1] = 'g';
      }
      else if((t + n) == ('r' + 'g')){
        seq[i] = seq[i+1] = 'b';
      }
      else{
        seq[i] = seq[i+1] = 'r';
      }
      if(dls(seq, depth-1)){
        return true;
      }
      seq[i] = t;
      seq[i+1] = n;
    }
  }
  return false;
}
void iddfs(char* seq){
  for(int depth = 0;depth <= 9; ++depth){
    if(dls(seq, depth)){
      cout << depth << endl;
      return;
    }
  }
  cout << "NA" << endl;
}
int main(){
  char seq[11];
  while(true){
    cin >> seq;
    if(seq[0] == '0'){
      break;
    }
    iddfs(seq);
  }
  return 0;
}