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 <string>
#include <queue>
#include <map>
using namespace std;

typedef pair<string,int> P;

string change(char a, char b) {
  string s;
  if((a=='r' && b=='g') || (a=='g' && b=='r')) s="bb";
  if((a=='r' && b=='b') || (a=='b' && b=='r')) s="gg";
  if((a=='g' && b=='b') || (a=='b' && b=='g')) s="rr";
  return s;
}

int main() {
  string t;
  while(cin >> t && t!="0") {
    map<string,int> color;
    queue<P> que;
    que.push(P(t,0));
    color[t]=1;
    int ans=-1;
    while(!que.empty()) {
      P p=que.front();
      que.pop();
      string s=p.first;
      bool ck=true;
      for(int i=0; i<s.size()-1; i++) {
	if(s[i]!=s[i+1]) {
	  string r;
	  r=s.substr(0,i)+change(s[i],s[i+1])+s.substr(i+2,s.size()-i-2);
	  if(color[r]!=1) {
	    que.push(P(r,p.second+1));
	    color[r]=1;
	  }
	  ck=false;
	}
      }
      if(ck) {
	ans=p.second;
	break;
      }
    }
    if(ans==-1) cout << "NA" << endl;
    else cout << ans << endl;
  }
  return 0;
}

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

typedef pair<string,int> P;

int main(){
  int kaku=0;
  string body;
  while(1){
  cin>>body;
  if(body=="0")return 0;
  map<string,int> used;
  queue<P> que;
  que.push(P(body,0));
  while(!que.empty()){
    P p =que.front();que.pop();
    string now = p.first;
    int co = p.second;
    int c=1;
    for(int i=0;i<body.size();i++){
      if(now[0]==now[i+1])c++;
    }
    if(c==body.size()){
      cout<<co<<endl;
      kaku=1;
      break;
    }
    if(used[now]==1)continue;
    used[now]=1;
    for(int i=0;i<body.size()-1;i++){
      string next=now;
    if(next[i]==next[i+1])continue;
    if((next[i]=='r' && next[i+1]=='b') || (next[i]=='b' && next[i+1]=='r')){
      next[i]='g';
      next[i+1]='g';
      que.push(P(next,co+1));
    }
    if((next[i]=='r' && next[i+1]=='g') || (next[i]=='g' && next[i+1]=='r')){
      next[i]='b';
      next[i+1]='b';
      que.push(P(next,co+1));
    }
    if((next[i]=='g' && next[i+1]=='b') || (next[i]=='b' && next[i+1]=='g')){
      next[i]='r';
      next[i+1]='r';
      que.push(P(next,co+1));
    }
  }
  }
  if(kaku==0)cout<<"NA"<<endl;
  kaku=0;
}
}