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 <algorithm>
#include <string>

using namespace std;

bool dfs(string str, int c)
{
	bool f = true;
	for(int i = 1; i < str.size(); i++){
		if(str[0] != str[i]){
			f = false;
			break;
		}
	}

	if(f){
		return f;
	}
	if(c == 0){
		return f;
	}
	
	char s, t, u;
	for(int i = 0; i < str.size()-1; i++){
		if(str[i] != str[i+1]){
			s = str[i];
			t = str[i+1];
			if((s == 'r' && t == 'b') || (s == 'b' && t == 'r')){
				u = 'g';
			} else if((s == 'r' && t == 'g') || (s == 'g' && t == 'r')){
				u = 'b';
			} else {
				u = 'r';
			}
			str[i] = str[i+1] = u;
			f = dfs(str, c-1);
			if(f){
				break;
			}
			str[i] = s;
			str[i+1] = t;
		}
	}
	
	return f;
}

int main()
{
	int t;
	string str;
	
	while(cin>>str){
		if(str == "0"){
			break;
		}
		
		for(t = 0; t <= 9; t++){
			if(dfs(str, t)){
				break;
			}
		}
		
		if(t > 9){
			cout << "NA" << endl;
		} else {
			cout << t << endl;
		}
	}
	
	return 0;
}

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

typedef pair<string, int> P;

int bfs(string worm){
	queue<P> que;
	que.push(P(worm, 0));

	map<string, int> d;
	
	while(!que.empty()){
		P p = que.front();
		que.pop();

		//?????????????????????continue
		if(d[p.first]) continue;

		string str = p.first;

		//??¨?????????????????????????????§??????
		bool flag = false;
		for(int i=0;i<str.size()-1;i++){
			if(str[i] != str[i+1]){
				flag = true;
				break;
			}
		}
		//????????????return
		if(!flag) return p.second;

		//???????????????????????\??¨
		d[p.first] = p.second;

		for(int i=0;i<str.size()-1;i++){
			//??£??????????????§????????°????????¨???
			if(str[i] != str[i+1]){
				char temp;
				string next;

				//temp?????????????????????????????£??\
				if(str[i] != 'b' && str[i+1] != 'b'){
					temp = 'b';
				}else if(str[i] != 'g' && str[i+1] != 'g'){
					temp = 'g';
				}else{
					temp = 'r';
				}

				//?????????????????????next?????°?????????
				next = str;
				next[i] = next[i+1] = temp;

				//?????\?????????????????\
				que.push(P(next, p.second+1));
			}
		}
	}
	return -1;
}

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

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

typedef pair<string,int> P;

int main()
{
  string body;
  int check = 0;

  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;
        check = 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(check == 0)cout << "NA" << endl;
    check = 0;
  }
}