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<string>
#include<queue>
#include<unordered_map>
#include<map>
#define P pair<string,int>
#define p pair<char,char>
using namespace std;

int main()
{
	map<p, char>M;
	M[p('b', 'g')] = 'r';
	M[p('g', 'b')] = 'r';
	M[p('b', 'r')] = 'g';
	M[p('r', 'b')] = 'g';
	M[p('r', 'g')] = 'b';
	M[p('g', 'r')] = 'b';
	string a;
    l:;
	while (cin >> a, a != "0") {
		unordered_map<string, int>U;
		queue<P>Q;
		Q.push(P(a, 1));
		while (Q.size()) {
			P c = Q.front(); Q.pop();
			bool d = true;
			for (int e = 1; e < c.first.length(); e++)if (c.first[e - 1] != c.first[e])d = false;
			if (d) { cout << c.second - 1 << endl; goto l; }
			for (int e = 1; e < c.first.length(); e++) {
				if (c.first[e - 1] != c.first[e]) {
					string copy = c.first;
					copy[e - 1] = copy[e] = M[p(c.first[e - 1], c.first[e])];
					if (U[copy] == 0) { U[copy] = c.second + 1; Q.push(P(copy,U[copy])); }
				}
			}
		}
		puts("NA");
	}
}

C++: #include <iostream>
#include <string>
#include <queue>
#include <map>
using namespace std;
typedef pair<string, int> P;

int main()
{
	string str;
	while(cin >> str){
		if(str == "0")
			break;
		int count = -1;
		map<string,bool> mp;
		queue<P> que;
		P p;p.first = str;p.second = 0;
		que.push(p);
		while(que.size()){
			P s = que.front();que.pop();
			if(mp.find(s.first)!=mp.end())
				continue;
			else
				mp[s.first] = true;
			bool is_all = true;
			for(unsigned i=1;i<s.first.size();i++){
				if(s.first[0] != s.first[i]){
					is_all = false;
					break;
				}
			}
			if(is_all){
				count = s.second;
			}

			int a=0;
			for(unsigned i=0;i<s.first.size()-1;i++){
				P ss = s;
				if((ss.first[i] != ss.first[i+1])){
					if((ss.first[i] == 'r' && ss.first[i+1] == 'g') || (ss.first[i] == 'g' && ss.first[i+1] == 'r')){
						ss.first[i] = 'b';ss.first[i+1] = 'b';
					}
					if((ss.first[i] == 'r' && ss.first[i+1] == 'b') || (ss.first[i] == 'b' && ss.first[i+1] == 'r')){
						ss.first[i] = 'g';ss.first[i+1] = 'g';
					}
					if((ss.first[i] == 'b' && ss.first[i+1] == 'g') || (ss.first[i] == 'g' && ss.first[i+1] == 'b')){
						ss.first[i] = 'r';ss.first[i+1] = 'r';
					}
					ss.second = s.second+1;
					que.push(ss);
				}
			}
		}
		if(count == -1)
			cout << "NA" << endl;
		else
			cout << count << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<map>
#include<queue>
using namespace std;
typedef pair<string,int> P;
char color[3] = {'r','g','b'};
string com[3];
string str;
int len;
int bfs();

int main(){
	while(1){
		cin >> str;
		if(str == "0") break;
		len = str.size();
		for(int i=0;i<3;i++){
			com[i] = "";
			for(int j=0;j<len;j++){
				com[i] += color[i];
			}
		}
		int ans = bfs();
		if(ans == -1) cout << "NA" << endl;
		else cout << ans << endl;
	}
}

int bfs(){
	queue<P> que;
	que.push(P(str,0));
	map<string,int> dp;
	while(!(que.empty())){
		P p = que.front(); que.pop();
		string now = p.first;
		int cou = p.second;
		for(int i=0;i<3;i++){
			if(now == com[i]) return cou;
		}
		if(dp[now]) continue;
		dp[now] = 1;
		for(int j=0;j<len-1;j++){
			if(now[j] != now[j+1]){
				string tmp = now;
				for(int k=0;k<3;k++){
					if(tmp[j] != color[k] && tmp[j+1] != color[k]){
						tmp[j] = color[k];
						tmp[j+1] = color[k];
						break;
					}
				}
				que.push(P(tmp,cou+1));
			}
		}
	}
	return -1;
}