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>
#include <set>

using namespace std;

int len;
string str;

bool check(string s){
  char ch = s[0];

  for(int i = 1 ; i < len ; i++){
    if(ch != s[i]) return false;
  }
  return true;
}

int bfs(){
  string ans;
  queue<string> Q;
  Q.push(str);

  bool found = false;
  set<string> used;
  used.insert(str);
  map<string,int> dist;
  dist[str] = 0;

  while(!Q.empty()){
    string s = Q.front(); Q.pop();
    
    if(check(s)){
      found = true;
      ans = s;
      break;
    }

    for(int i = 1 ; i < len ; i++){
      string next = s;
      if(s[i-1] == 'b' && s[i] == 'r' ||
	 s[i-1] == 'r' && s[i] == 'b'){
	next[i-1] = next[i] = 'g';
      }else if(s[i-1] == 'b' && s[i] == 'g' ||
	       s[i-1] == 'g' && s[i] == 'b'){
	next[i-1] = next[i] = 'r';
      }else if(s[i-1] == 'r' && s[i] == 'g' ||
	       s[i-1] == 'g' && s[i] == 'r'){
	next[i-1] = next[i] = 'b';
      }
      
      if(!used.count(next)){
	dist[next] = dist[s] + 1;
	used.insert(next);
	Q.push(next);
      }
    }
  }

  if(!found) return -1;
  return dist[ans];
}

int main(){
  while(cin >> str,str != "0"){
    len = (int)str.size();
    int res = bfs();
    if(res == -1){
      cout << "NA" << endl;
    }else{
      cout << res << endl;
    }
  }
  return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<string>
#include<map>
using namespace std;
map<string, int> cache;
bool same(string seq){
  for(int i = 0; seq[i+1] != '\0'; ++i){
    if(seq[i] != seq[i+1]){
      return false;
    }
  }
  return true;
}
int dls(string seq, int depth){
  if(depth<0){
    return false;
  }
  if(same(seq)){
    return true;
  }
  if(cache.find(seq) != cache.end()){
    if(cache[seq] >= depth){
      return false;
    }
    cache[seq] = depth;
  }
  else{
    cache[seq] = depth;
  }
  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(string seq){
  cache = map<string, int>();
  for(int depth = 0;depth <= 20; ++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;
}

C++: #define	_USE_MATH_DEFINES
#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cfloat>
#include <map>
#include <queue>
#include <stack>
#include <list>
#include <string>
#include <set>
using namespace std;
int main(){
	
	string s;
	while(cin>>s,s!="0"){
		set<string> seto;
		queue<string> q; 
		int count=0;
		bool f=false;
		q.push(s);
		seto.insert(s);
		while(!q.empty()){
			int k=q.size();
			while(k>0){
			string n=q.front();
					 f=true;
			for(int i=0;i<s.size();i++){
				if(n[0]!=n[i]){
					f=false;
					break;
				}
				
			}
				if(f)
					break;
			for(int i=0;i<s.size()-1;i++){
				string n=q.front();
				if(n[i]=='r'&&n[i+1]=='b'||n[i]=='b'&&n[i+1]=='r'){
						n[i]='g';
						n[i+1]='g';
				}
				else if(n[i]=='b'&&n[i+1]=='g'||n[i]=='g'&&n[i+1]=='b'){
						n[i]='r';
						n[i+1]='r';
				}
				else if(n[i]=='r'&&n[i+1]=='g'||n[i]=='g'&&n[i+1]=='r'){
						n[i]='b';
						n[i+1]='b';
				}
				set<string>::iterator a=seto.find(n);
				if(a==seto.end()){
					q.push(n);
					seto.insert(n);
					
				}
				}
				q.pop();
				k--;
			}
			if(f){
				
				break;
			}
			else{
				count++;
			}
		}
		if(f)
			cout<<count<<endl;
		else
			cout<<"NA"<<endl;
		
			
	}
	
	
}