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<complex>
#include<algorithm>
#include<iostream>
#include<iomanip>
#include<cmath>
#include<vector>
#include<map>
#include<sstream>
#include<ctime>
#include<cstdio>
#include<cstdlib>
#include<cassert>
#include<deque>
#include<queue>
#include<climits>
#include<list>
#include<stack>
#include<ctime>
#define all(n) n.begin(),n.end()
#define REP(i,s,n) for(int i=s;i<n;i++)
#define rep(i,n) REP(i,0,n)
#define insert(a,b,c,d) PP(P(a,b),P(c,d))
#define F first
#define S second
#define Iter(c) __typeof__((c).begin())
#define foreach(i,c) for(Iter(c) i = (c).begin();i != (c).end();++i)
#define pb push_back
#define INF (1<<27)
#define EPS 1e-10
#define equals(a,b) (fabs((a)-(b)) < EPS)

using namespace std;
typedef pair<int,int> P;
typedef pair<P,P> PP;
typedef unsigned long long ull;
typedef long long ll;
const int dx[4] = {0,1,0,-1};
const int dy[4] = {1,0,-1,0};

typedef pair<string,int> SI;

bool ok(string s)
{
  char c = s[0];
  for(int i=0;i<s.length();i++)
    if(c != s[i])
      return false;
  return true;
}

char getc(char c,char cc)
{
  map<char,bool> index;
  index['r'] = false,index['b'] = false,index['g'] = false;
  index[c] = true;
  index[cc] = true;
  foreach(i,index)
    if(!(*i).S)
      return (*i).F;

}

int solve(string s)
{

  queue<SI> que;
  que.push(SI(s,0));
  map<string,bool> used;
  while(!que.empty())
    {
      SI si = que.front(); que.pop();

      if(used[si.F])
	continue;

      used[si.F] = true;
 
      if(ok(si.F))
	{
	  return si.S;
	}

      if(si.S > 20)
	continue;

      rep(i,si.F.length()-1)
	{
	  if(si.F[i] == si.F[i+1])
	    continue;
	  string news = si.F;
	  news[i] = news[i+1] = getc(si.F[i],si.F[i+1]);
	  que.push(SI(news,si.S+1));
	}

    }

  return -1;
}


int main(){

  while(true)
    {
      string s;
      cin >> s;
      if(s[0] == '0')
	break;

      int ans = solve(s);
      ans != -1?cout << ans << endl:cout << "NA" << endl;

    }

return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;

int main(){
  while(true){
    string s;
    cin>>s;
    if(s[0]=='0')break;
    string sr(s.size(),'r');
    string sg(s.size(),'g');
    string sb(s.size(),'b');
    map<string,int> mp;
    queue<string> q;
    q.push(s);
    mp[s]=0;
    int f=0;
    for(int i=0;i<1e3;i++){
      string x=q.front();
      q.pop();
      for(int j=0;j<s.size()-1;j++){
        string y=x;
        if(y[j]=='r'&&y[j+1]=='g'){
          y[j]='b';
          y[j+1]='b';
        }
        if(y[j]=='b'&&y[j+1]=='g'){
          y[j]='r';
          y[j+1]='r';
        }
        if(y[j]=='r'&&y[j+1]=='b'){
          y[j]='g';
          y[j+1]='g';
        }
        if(y[j]=='g'&&y[j+1]=='b'){
          y[j]='r';
          y[j+1]='r';
        }
        if(y[j]=='g'&&y[j+1]=='r'){
          y[j]='b';
          y[j+1]='b';
        }
        if(y[j]=='b'&&y[j+1]=='r'){
          y[j]='g';
          y[j+1]='g';
        }
        //cout<<mp[x]+1<<" "<<y<<endl;
        if(y==sr||y==sb||y==sg){
          cout<<mp[x]+1<<endl;
          f=1;
          break;
        }
        if(mp[y]==0){
          mp[y]=mp[x]+1;
          q.push(y);
        }
      }
      if(f)break;
    }
    if(!f)cout<<"NA"<<endl;
  }
}

C++: #include <iostream>
#include <utility>
#include <string>
#include <queue>
#include <set>
using namespace std;
#define P pair<string,int>
#define C(X)((X)=='r'?0:(X)=='b'?1:2)
int main() {
	string w;
	while(cin>>w,w!="0") {
		queue<P> q;
		set<string> s;
		q.push(P(w,0));
		s.insert(w);
		bool OK=false;
		while(!q.empty()) {
			P p=q.front();q.pop();
			bool ok=true;
			for(int i=1;i<p.first.size();i++) {
				if(p.first[i-1]!=p.first[i]) {
					ok=false;break;
				}
			}
			if(ok) {
				cout<<p.second<<endl;
				OK=true;break;
			}
			for(int i=1;i<p.first.size();i++) {
				if(p.first[i-1]!=p.first[i]) {
					string ns=p.first;
					bool chr[3]={0};
					chr[C(ns[i-1])]=true;
					chr[C(ns[i])]=true;
					for(int j=0;j<3;j++) {
						if(chr[j]==false) {
							ns[i-1]=ns[i]=(j==0?'r':j==1?'b':'g');
						}
					}
					if(s.find(ns)==s.end()) {
						q.push(P(ns,p.second+1));
						s.insert(ns);
					}
				}
			}
		}
		if(OK==false)cout<<"NA"<<endl;
	}
}