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 <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
using namespace std;
#define INF 100000000
typedef long long ll;

int main(void) {
    while (1) {
        string s;
        cin >> s;
        if (s == "0") break;
        map<string, int> mi;
        queue<string> q;
        q.push(s);
        mi[s] = 0;
        bool flag = true;
        while (!q.empty()) {
            string now = q.front(); q.pop();
            // 全て同じ文字かどうかのチェック
            int i;
            for (i = 0; i < now.size()-1; i++) {
                if (now[i] != now[i+1]) {
                    break;
                }
            }
            if (i == now.size()-1) {
                cout << mi[now] << endl;
                flag = false;
                break;
            }
            // いろいろ移行するところを考える
            for (int i = 0; i < now.size()-1; i++) {
                string s = now;
                if (s[i] != s[i+1]) {
                    if (s[i] != 'r' && s[i+1] != 'r') {
                        s[i] = 'r'; s[i+1] = 'r';
                    } else if (s[i] != 'g' && s[i+1] != 'g') {
                        s[i] = 'g'; s[i+1] = 'g';
                    } else {
                        s[i] = 'b'; s[i+1] = 'b';
                    }
                }
                if (mi.find(s) == mi.end()) {
                    q.push(s);
                    mi.insert(map<string, int>::value_type(s, mi[now]+1));
                }
            }
        }
        if (flag) cout << "NA" << endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)

map<char, int> m;
map<string, int> ans;
char c[3] = {'r', 'g', 'b'};

int main() {
	REP(i, 3) m[c[i]] = 1<<i;
	
	string str;
	while (cin >> str, str != "0") {
		string ser[3] = {};
		REP(i, 3) REP(j, str.size()) {
			ser[i] += c[i];
		}
		
		queue<pair<int, string> > que;
		REP(i, 3) que.push(make_pair(0, ser[i]));
		
		while (!que.empty()) {
			int t = que.front().first;
			string now = que.front().second;
			que.pop();
			
			if (ans.find(now) != ans.end()) continue;
			ans[now] = t;
			
			REP(i, now.size() - 1) {
				if (now[i] == now[i + 1]) {
					string next = now;
					int nextcor = 7 - m[now[i]];
					vector<char> pl;
					REP(j, 3) if (nextcor & (1<<j)) pl.push_back(c[j]);
					REP(j, 2) {
						next[i] = pl[j];
						next[i + 1] = pl[(j + 1) % 2];
						que.push(make_pair(t + 1, next));
					}
				}
			}
		}
		if (ans.find(str) == ans.end()) puts("NA");
		else cout << ans[str] << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <queue>
#include <map>
#include <cstring>
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();

    if(d[p.first])  continue;

    string str = p.first;

    bool flag = true;
    for(int i = 0; i < str.size()-1; i++){
      if(str[i] != str[i+1]){
        flag = false;
        break;
      }
    }

    if(flag) return p.second;

    for(int i = 0; i < str.size()-1; i++){
      if(str[i] != str[i+1]){
        string next;
        char tmp;
        if(str[i] != 'r' && str[i+1] != 'r'){
          tmp = 'r';
        }else if(str[i] != 'b' && str[i+1] != 'r'){
          tmp = 'b';
        }else{
          tmp = 'g';
        }

        next = str;
        next[i] = next[i+1] = tmp;
        que.push(P(next, p.second+1));
      }
    }
  }
  return -1;
}

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

  return 0;
}

C++: #include<iostream>
#include<string>
#include<queue>
#include<set>
#include<utility>
using namespace std;
char C(char a,char b)
{
	if(a!='r'&&b!='r')return'r';
	if(a!='g'&&b!='g')return'g';
	return'b';
}
int F(string s)
{
	int i,b;
	string n;
	set<string> h;
	typedef pair<string,int>T;
	queue<T> q;	
	T p;
	q.push(make_pair(s,0));
	while(!q.empty())
	{
		p=q.front();q.pop();
		s=p.first;
		if(!h.insert(s).second)continue;
		for(b=1,i=0;i+1<s.size();++i)
			if(s[i]!=s[i+1])b=0;
		if(b) return p.second;

		for(i=0;i+1<s.size();++i)
		{
			if(s[i]!=s[i+1])
			{
				n=s;
				n[i]=n[i+1]=C(n[i],n[i+1]);
				q.push(make_pair(n,p.second+1));
			}
		}
	}
	return -1;
}
int main()
{
	string s;
	int n;
	while(cin>>s,s[0]-'0')
		if((n=F(s))<0) cout<<"NA\n";
		else cout<<n<<endl;
	return 0;
}