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 <vector>
#include <string>
#include <set>
#include <queue>

#define rep(i,a) for(int i = 0 ; i < a ; i ++)

using namespace std;

int main(void){
  string s;
  cin>>s;
  set<string> se;
  queue<pair<string,int> > q;
  se.insert(s);
  q.push(make_pair(s,0));
  int cnt = 10;
  char a[3] = {'r','g','b'};
  string ans[3];
  rep(i,3){
    rep(j,s.size()){
      ans[i] += a[i];
    }
    //cout<<ans[i]<<endl;
  }
  bool find = true;
  while(true){
    if(q.size()==0)break;
//    cout<<q.front().first<<" "<<q.front().second<<endl;
    pair<string,int> qq = q.front(); q.pop();
    string ss = qq.first;
    int n = qq.second;
    if(ss.size()==s.size()+2 ){
      break;
    }
    cnt ++;
    bool f = false;
    rep(i,3){
      if(ans[i] == ss){
        f = true;
        find = false;
        break;
      }
    }
    if(f)break;
    n++;
    rep(i,ss.size()-1){
      if(ss[i] != ss[i+1]){
        if((ss[i] == a[0] && ss[i+1] == a[1]) || (ss[i] == a[1] && ss[i+1] == a[0])){
          string word = ss.substr(0,i) + a[2] + a[2] + ss.substr(i+2,ss.size()-i+2);
          if(se.find(word) != se.end())continue;
          se.insert(word);
          q.push(make_pair(word,n));
          se.insert(word);
        }
        if((ss[i] == a[0] && ss[i+1] == a[2]) || (ss[i] == a[2] && ss[i+1] == a[0])){
          string word = ss.substr(0,i) + a[1] + a[1] + ss.substr(i+2,ss.size()-i+2);
          if(se.find(word) != se.end())continue;
          se.insert(word);
          q.push(make_pair(word,n));
          se.insert(word);
        }
        if((ss[i] == a[2] && ss[i+1] == a[1]) || (ss[i] == a[1] && ss[i+1] == a[2])){
          string word = ss.substr(0,i) + a[0] + a[0] + ss.substr(i+2,ss.size()-i+2);
          if(se.find(word) != se.end())continue;
          se.insert(word);
          q.push(make_pair(word,n));
          se.insert(word);
        }
      }
    }
  }
  if(find)cout<<"NA"<<endl;
}

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

#define ALL(a) (a).begin(). (a).end()

using namespace std;

int other(int x, int y){
	if(x > y)return other(y,x);
	if(x == 0 && y == 1)return 2;
	if(x == 0 && y == 2)return 1;
	if(x == 1 && y == 2)return 0;
}

int main(){
	while(true){
		string str; cin >> str;
		if(str == "0")break;
		vector<int> b(str.size());
		for(int i = 0; i < str.size(); i++){
			switch(str[i]){
				case 'r':
					b[i] = 0;
					break;
				case 'g':
					b[i] = 1;
					break;
				case 'b':
					b[i] = 2;
					break;
			}
		}
		int ans = -1;
		queue<vector<int> > q;
		map<vector<int> , int> m;
		q.push(b);
		m[b] = 0;
		while(!q.empty()){
			auto t = q.front();
			q.pop();
			int c = t[0];
			bool flag = true;
			for(auto e : t){
				if(e != c){
					flag =false;
					break;
				}
			}
			if(flag){
				ans = m[t];
				break;
			}
			
			for(int i = 1; i < t.size(); i++){
				auto tt = t;
				if(t[i] != t[i-1]){
					tt[i] = tt[i-1] = other(t[i], t[i-1]);
				}
				if(m.find(tt) == m.end()){
					q.push(tt);
					m[tt] = m[t]+1;
				}
			}
		}
		if(ans == -1){
			cout << "NA" << endl;
		}
		else{
			cout << ans << endl;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <queue>
#include <string>
#include <map>
using namespace std;

struct worm{
	int c;
	string s;
};
queue<worm> que;
bool str_check(string str){
	for(int i = 1;i < str.size();++i){
		if(str[0] != str[i]) return false;
	}
	return true;
}
int f(){
	map<string,int> check;
	while(que.size()){
		worm w = que.front(),tmp;
		que.pop();
		int n = w.c;
		string str = w.s;
		if(str_check(str)){
			return n;
		}
		for(int i = 0;i < str.size() - 1;++i){
			if(str[i] != str[i+1]){
				if((str[i] == 'r' && str[i+1] == 'b') || (str[i] == 'b' && str[i+1] == 'r')){
					str[i] = str[i+1] = 'g';
				}
				else if((str[i] == 'g' && str[i+1] == 'b') || (str[i] == 'b' && str[i+1] == 'g')){
					str[i] = str[i+1] = 'r';
				}
				else {
					str[i] = str[i+1] = 'b';
				}

				if(!check.count(str)){
					tmp.s = str;
					tmp.c = n + 1;
					que.push(tmp);
					check[str] = n + 1;
				}
				str = w.s;
			}
		}
	}
	return -1;
}
int main(){
	string str;
	worm w;
	while(cin >> str){
		if(str == "0") break;
		w.s = str;
		w.c = 0;
		que.push(w);
		int n = f();
		if(n == -1) cout << "NA\n";
		else cout << n << endl;
		while(que.size()){
			que.pop();
		}
	}
	return 0;
}