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 <vector>
#include <queue>
#include <string>
#include <cstdio>
using namespace std;

#define loop(i, n) for (int i = 0; i < n; i++)
#define INF 1010001000

typedef long long int ll;

ll tr(string a);
bool cl(string a);
int c3(ll a);
int solve(string st);

int main()
{
    string input;
    cin >> input;
    while (input[0] != '0') {
        int ans = solve(input);
        if (ans != INF) {
            cout << ans << endl;
        } else {
            cout << "NA" << endl;
        }
        cin >> input;
    }
    return 0;
}

int solve(string st)
{
    int ans = 0;
    vector<bool> check(1048576, false);
    queue<string> a, b, c;
    if ( cl(st) ) {
        return ans;
    }
    a.push(st);
    while (!a.empty()) {
        while (!a.empty()) {
            st = a.front();
            a.pop();
            if (check[c3(tr(st))]) {
                continue;
            } else {
                check[c3(tr(st))] = true;
                //cout << c3(tr(st)) << endl;
            }
            if (cl(st)) {
                return ans;
            }
            for (int i = 1; i < st.size(); i++) {
                if (st[i-1] != st[i]) {
                    string nw(st);
                    if (st[i-1] != 'r' && st[i] != 'r') {
                        nw[i-1] = 'r';
                        nw[i] = 'r';
                    } else if (st[i-1] != 'g' && st[i] != 'g') {
                        nw[i-1] = 'g';
                        nw[i] = 'g';
                    } else if (st[i-1] != 'b' && st[i] != 'b') {
                        nw[i-1] = 'b';
                        nw[i] = 'b';
                    }
                    b.push(nw);
                }
            }
        }
        a = b;
        b = c;
        ans++;
    }
    return INF;
}

ll tr(string a)
{
    ll ret = 0;
    for (int i = 0; i < a.size(); i++) {
        ret *= 10;
        if (a[i] == 'r') {
            ret += 1;
        } else if (a[i] == 'g') {
            ret += 2;
        } else {
            ret += 3;
        }
    }
    return ret;
}

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

int c3(ll a)
{
    int ret = 0;
    if (a) {
        ret = c3(a / 10);
        ret *= 4;
        ret += a % 10;
    }
    return ret;
}

C++: #include<queue>
#include<map>
using namespace std;
#define INFTY (1<<21)

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

char getColor( char c1, char c2 ){
    if ( c1 == 'g' ) return (c2=='r' ? 'b' : 'r');
    else if ( c1 == 'b' ) return (c2=='r' ? 'g' : 'r');
    else if ( c1 == 'r' ) return (c2=='b' ? 'g' : 'b');
}

int bfs(string s){
    queue<string> Q;
    map<string, bool> V;
    map<string, int> D;

    Q.push(s);
    V[s] = true;
    D[s] = 0;
    string u, v;
    
    while(!Q.empty()){
        u = Q.front(); Q.pop();
        if ( isSameColor(u) ) return D[u];
        for ( int i = 1; i < u.size(); i++ ){
            if ( u[i-1] != u[i] ){
                v = u;
                v[i-1] = v[i] = getColor(u[i-1], u[i]);
                if ( !V[v] ){
                    V[v] = true;
                    D[v] = D[u] + 1;
                    Q.push(v);
                }
            }
        }
    }

    return INFTY;
}

int main(){
    string initial;
    while( cin >> initial ){
        if ( initial == "0" ) break;
        int cost = bfs( initial );
        if ( cost == INFTY ) cout << "NA" << endl;
        else cout << cost << endl;
    }
    return 0;
}