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 <cstdio>
#include <algorithm>
#include <vector>
#include <sstream>
#include <cmath>
#include <queue>

#define INF (1 << 21)

using namespace std;

int N;

int check[100000];

queue<string> que, que_next;

int index(string str){
	
	int ref = 0;
	
	for(int i = 0; i < N; i++){
		ref *= 3;
		ref += str[i] - '0';
	}
	
	return ref;
}

int main(){
	
	while(true){
		string str;
		cin >> str;
		
		queue<string> que_emp;
		
		que = que_emp;
		que_next = que_emp;
		
		for(int i = 0; i < 100000; i++){
			check[i] = INF;
		}
		
		if(str[0] == '0'){
			break;
		}else{
			N = str.size();
			for(int i = 0; i < N; i++){
				if(str[i] == 'r'){
					str[i] = '0';
				}else if(str[i] == 'b'){
					str[i] = '1';
				}else{
					str[i] = '2';
				}
			}
		}
		
		que.push(str);
		
		int depth = 0;
		
		while(true){
			while(!que.empty()){
				string str = que.front();
				que.pop();
				if(check[index(str)] != INF){
					continue;
				}
				check[index(str)] = depth;
				for(int i = 0; i < N - 1; i++){
					if(str[i] != str[i + 1]){
						string str_copy = str;
						if(str[i] != '0' && str[i + 1] != '0'){
							str_copy[i] = '0';
							str_copy[i + 1] = '0';
						}else if(str[i] != '1' && str[i + 1] != '1'){
							str_copy[i] = '1';
							str_copy[i + 1] = '1';
						}else{
							str_copy[i] = '2';
							str_copy[i + 1] = '2';
						}
						que_next.push(str_copy);
					}
				}
			}
			que = que_next;
			que_next = que_emp;
			depth++;
			if(que.empty()){
				break;
			}
			//cout << depth << " " << que.size() << endl;;
		}
		
		string check_0 = "";
		string check_1 = "";
		string check_2 = "";
		
		for(int i = 0; i < N; i++){
			check_0 = check_0 + "0";
			check_1 = check_1 + "1";
			check_2 = check_2 + "2";
		}
		
		int ans = min(min(check[index(check_0)], check[index(check_1)]), check[index(check_2)]);
		
		if(ans == INF){
			cout << "NA" << endl;
		}else{
			cout << ans << 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;
    if(s==sr||s==sb||s==sg){
      cout<<0<<endl;
    }else{
      //for(int i=0;i<1e6;i++){
      while(!q.empty()){
        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!=1)cout<<"NA"<<endl;
    }
  }
}

C++: #include<cstdio>
#include<iostream>
#include<string>
#include<map>
#include<queue>

using namespace std;

#define rep(i,n) for(int i=0;i<n;i++)
#define reps(i,n) for(int i=1;i<=n;i++)

class S{
	public:
	
	string a;
	int b;
	
	S(){}
	S(string a,int b):a(a),b(b){}
};


char nn[333][333];

int main(){
	
	nn['r']['g']='b';
	nn['g']['r']='b';
	
	nn['g']['b']='r';
	nn['b']['g']='r';
	
	nn['b']['r']='g';
	nn['r']['b']='g';
	
	while(1){
		string a;
		cin>>a;
		
		if(a=="0")break;
		
		map<string,int> ch;
		
		queue<S> que;
		que.push(S(a,0));
		
		while(1){
			if(que.empty()){
				cout<<"NA"<<endl;
				break;
			}
			
			S u = que.front();
			que.pop();
			
			if(ch[u.a]==1)continue;
			ch[u.a]=1;
			
			int flg=1;
			rep(i,u.a.size()-1){
				if(u.a[i] != u.a[i+1]){
					flg=0;
					break;
				}
			}
			if(flg==1){
				cout<<u.b<<endl;
				break;
			}
			
			rep(i,u.a.size()-1){
				if(u.a[i]!=u.a[i+1]){
					string b = u.a;
					b[i] = nn[u.a[i]][u.a[i+1]];
					b[i+1] = nn[u.a[i]][u.a[i+1]];
					
					que.push(S(b,u.b+1));
				}
			}
			
		}
	}
}