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

map<char, char> rot = {
    {'r', 'g'}, {'g', 'b'}, {'b', 'r'}
};
map<string, bool> used;

void rotate(string &s) {
    for (int i=0; i<(int)s.size(); ++i) s[i] = rot[s[i]];
}

int main() {
    string s;
    while (cin >> s, s != "0") {
        used.clear();
        string r = "", g = "", b = "";
        for (int i=0; i<(int)s.size(); ++i) {
            r += "r"; g += "g"; b += "b";
        }
        queue<pair<string,int> > q;
        q.push(make_pair(s, 0));
        int res = -1;
        while ( ! q.empty()) {
            string col = q.front().first;
            used[col] = true; rotate(col);
            used[col] = true; rotate(col);
            used[col] = true; rotate(col);
            int t = q.front().second;
            if (col == r || col == g || col == b) {
                res = t;
                break;
            }
            q.pop();
            for (int i=0; i<(int)col.size()-1; ++i) {
                if (col[i] != col[i+1]) {
                    string nxt = col;
                    if (col[i] != 'r' && col[i+1] != 'r') {
                        nxt[i] = 'r'; nxt[i+1] = 'r';
                    } else if (col[i] != 'g' && col[i+1] != 'g') {
                        nxt[i] = 'g'; nxt[i+1] = 'g';
                    } else if (col[i] != 'b' && col[i+1] != 'b') {
                        nxt[i] = 'b'; nxt[i+1] = 'b';
                    }
                    if ( ! used[nxt]) {
                        q.push(make_pair(nxt, t+1));
                    }
                }
            }
        }
        if (res < 0) {
            cout << "NA" << endl;
        } else {
            cout << res << endl;
        }
    }
    return 0;
}

C++: #include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string>
#include <cstring>
#include <cmath>
#include <complex>
#include <map>
#include <set>
#include <climits>
using namespace std;

#define rep(i,n) for(int i=0;i<int(n);++i)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define EPS 1e-8
#define F first
#define S second

static const double PI=6*asin(0.5);
typedef long long ll;
typedef complex<double> CP;
typedef pair<int,int> P;
static const int INF=1<<24;

string s;
string qf;
set<string> vis;

bool check(string a){
	char t=a[0];
	rep(i,a.size()){
		if(t!=a[i]) return false;
	}
	return true;
}

int main(){
	
	while(cin>>s,s[0]!='0'){
		//cout<<s<<endl;
		vis.clear();
		int ans=-1;
		queue<string> qu;
		if(check(s)){
			cout<<"0"<<endl;
			continue;
		}
		vis.insert(s);
		qu.push(s);
		bool f1=false;
		bool f2=false;
		bool f3=false;
		while(!qu.empty()){
			f1=false;
			f2=false;
			ans++;
			int qs=qu.size();
			rep(i,qs){
				qf=qu.front();
				qu.pop();
				rep(j,s.size()-1){
					if(qf[j]!=qf[j+1]){
						string tmp=qf;
						tmp[j] = tmp[j+1] = 'r'+'g'+'b'-qf[j]-qf[j+1];
						if(vis.find(tmp)==vis.end()){
							qu.push(tmp);
							vis.insert(tmp);
							f1=true;
							if(check(tmp)) f3=true;
						}
						f2=true;
					}
				}
			}
			if(f3) break;
		}
		if(f3) cout<<ans+1<<endl;
		else cout<<"NA"<<endl;
		
	}
	
	return 0;
}