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;
  while(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 <iostream>
#include <cstdio>
#include <algorithm>
#include <cassert>
#include <vector>
#include <string>
#include <cmath>
#include <map> 
#include <sstream>
#include <cstdio>
#include <complex>
#include <cstring>
#include <queue>
using namespace std;
 
const int MAX= 10000100;

#define loop(i,a,b) for(int i = a ; i < b ; i ++)
#define rep(i,a) loop(i,0,a)
#define all(a) (a).begin(),(a).end()
#define ll long long int
#define gcd(a,b) __gcd(a,b)
#define pb(a) push_back(a)
int GCD(int a, int b) {if(!b) return a; return gcd(b, a%b);}
int lcm(int a, int b) {return a*b / gcd(a, b);}
typedef pair<string ,int> P;

int bfs(string s){
  queue<P> que;
  que.push(P(s,0));
  
  map<string,int> d;
  while(!que.empty()){
    P p=que.front();
    que.pop();
    
    if(d[p.first])continue;
    string st = p.first;
    
    bool f = false;
    rep(i,st.size()-1){
      if(st[i]!=st[i+1]){ // find different words
	f = true;
	break;
      }
    }

    if(!f)return p.second;
    
    d[p.first] = second;
    rep(i,st.size()-1){
      if(st[i] != st[i+1]){
	char t;
	string nx;
      }
    }
    
  }
  
}

int main(void){
  string s;
  while(cin>>s,s!="0"){
    int ret = bfs(s);
    if(ret>=0)cout<<ret<<endl;
    else cout<<"NA"<<endl;
  }
}

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;
		m[p.first] = 1;
		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;
}