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<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;
int que[60000][10],flg[1050000];
int main(void){
	int p1,p2,i,j,len,time[60000],copy[10],f,x,ans,iro;
	char ca[11];
	while(1){
		cin>>ca;
		if(ca[0]=='0') break;
		len=strlen(ca);
		for(i=0;i<len;i++){
			if(ca[i]=='r') que[0][i]=0;
			if(ca[i]=='g') que[0][i]=1;
			if(ca[i]=='b') que[0][i]=2;
		}
		for(i=0;i<=1050000;i++) flg[i]=0;
		p1=0; p2=1; time[0]=0; ans=-1;
		while(1){
			if(p1==p2){
//				cout<<p1<<endl;
				break;
			}
/*			cout<<p1<<' ';
			for(i=0;i<len;i++) cout<<que[p1][i];
			cout<<' '<<time[p1]<<endl;*/
			f=1;
			for(i=0;i<len-1;i++){
				if(que[p1][i]!=que[p1][i+1]){
					f=0;
					break;
				}
			}
			if(f==1){
				ans=time[p1];
				break;
			}
			for(i=0;i<len-1;i++){
				for(j=0;j<len;j++) copy[j]=que[p1][j];
				if(copy[i]!=copy[i+1]){
					iro=copy[i]+copy[i+1];
					if(iro==3){
						copy[i]=0; copy[i+1]=0;
					}
					if(iro==2){
						copy[i]=1; copy[i+1]=1;
					}
					if(iro==1){
						copy[i]=2; copy[i+1]=2;
					}
				}
				x=copy[0];
				for(j=1;j<len;j++) x=x*4+copy[j];
				if(flg[x]==0){
					flg[x]=1; time[p2]=time[p1]+1;
					for(j=0;j<len;j++) que[p2][j]=copy[j];
					p2++;
				}
			}
			p1++;
		}
		if(ans==-1) cout<<"NA"<<endl;
		else cout<<ans<<endl;
	}
	return 0;
}

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

using namespace std;

int main()
{
	string s;
	while (cin >> s, s[0] != '0') {
		map<string, bool> m;

		queue<string> q, r;

		q.push(s);

		int cnt = 0;

		while (q.size()) {
			while (q.size()) {
				string t = q.front(); q.pop();
				if (m[t]) continue;
				m[t] = true;
				bool f = true;
				for (int i = 0; i < t.size() - 1; ++i) {
					if ((t[i] == 'r' && t[i + 1] == 'b') || (t[i] == 'b' && t[i + 1] == 'r')) {
						char c = t[i], d = t[i + 1];
						t[i] = t[i + 1] = 'g';
						r.push(t);
						t[i] = c, t[i + 1] = d;
						f = false;
					} else if ((t[i] == 'b' && t[i + 1] == 'g') || (t[i] == 'g' && t[i + 1] == 'b')) {
						char c = t[i], d = t[i + 1];
						t[i] = t[i + 1] = 'r';
						r.push(t);
						t[i] = c, t[i + 1] = d;
						f = false;
					} else if ((t[i] == 'r' && t[i + 1] == 'g') || (t[i] == 'g' && t[i + 1] == 'r')) {
						char c = t[i], d = t[i + 1];
						t[i] = t[i + 1] = 'b';
						r.push(t);
						t[i] = c, t[i + 1] = d;
						f = false;
					}
				}
				if (f) {
					cout << cnt << endl;
					goto nxt;
				}
			}
			while (r.size()) {
				string t = r.front(); r.pop();
				q.push(t);
			}
			cnt++;
		}

		cout << "NA" << endl;
nxt:;
	}
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef vector<int> vi;
typedef vector<vi> vii;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<vb> vbb;
typedef pair<int, int> pii;
typedef long long ll;
typedef unsigned long long ull;

#define all(a)  (a).begin(),(a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair

#define loop(i,a,b) for(int i=(a);i<ull(b);++i)
#define rep(i,n) loop(i,0,n)

const double eps = 1e-10;
const double pi  = acos(-1.0);
const double inf = (int)1e8;

bool check(string s){
    for(int i=0; i< s.size()-1; i++) if(s[i] != s[i+1]) return false;
    return true;
}

vector<string> v;

bool emergence(string s){
    for(int i=0; i< v.size(); i++) if(v[i] == s) return true;
    else return false;
}

int main(){
    string s;
    while(cin >> s, s!= "0"){
        v.clear();
        queue<pair<string, int> > que;
        que.push(make_pair(s, 0));
        int ret = 9;
        while(que.size()){
            s = que.front().first; int count = que.front().second; que.pop();

            if(ret < count) continue;
            if(check(s))ret = count;
            if(emergence(s)) continue;
            else v.push_back(s);

            for(int i=0; i< s.size()-1; i++){
                if(s[i] != s[i+1]){
                    string t = s.substr(i, 2);
                    sort(t.begin(),t.end());
                    if(t == "br") t = "gg";
                    else if(t == "bg") t = "rr";
                    else if(t == "gr") t = "bb";
                    que.push(make_pair(s.substr(0, i)+t+s.substr(i+2), count+1));
                }
            }
        }
        if(ret == 9) cout << "NA" << endl;
        else cout << ret << endl;
    }
}