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 "bits/stdc++.h"
using namespace std;

int main(){
  while(true){
    string s;
    cin>>s;
    if(s=="0")break;
    string sr(s.size(),'r');
    string sg(s.size(),'g');
    string sb(s.size(),'b');
    map<string,int> mp;
    queue<string> q;
    q.push(s);
    mp[s]=0;
    int f=0;
    if(s==sr||s==sb||s==sg){
      cout<<0<<endl;
    }else{
      //for(int i=0;i<1e6;i++){
      while(!q.empty()){
        string x=q.front();
        q.pop();
        for(int j=0;j<s.size()-1;j++){
          string y=x;
          if(y[j]=='r'&&y[j+1]=='g'){
            y[j]='b';
            y[j+1]='b';
          }else if(y[j]=='b'&&y[j+1]=='g'){
            y[j]='r';
            y[j+1]='r';
          }else if(y[j]=='r'&&y[j+1]=='b'){
            y[j]='g';
            y[j+1]='g';
          }else if(y[j]=='g'&&y[j+1]=='b'){
            y[j]='r';
            y[j+1]='r';
          }else if(y[j]=='g'&&y[j+1]=='r'){
            y[j]='b';
            y[j+1]='b';
          }else if(y[j]=='b'&&y[j+1]=='r'){
            y[j]='g';
            y[j+1]='g';
          }
          //cout<<mp[x]+1<<" "<<y<<endl;
          if(y==sr||y==sb||y==sg){
            cout<<mp[x]+1<<endl;
            f=1;
            break;
          }
          if(mp.count(y)==0){
            mp[y]=mp[x]+1;
            q.push(y);
          }
        }
        if(f)break;
      }
      if(!f)cout<<"NA"<<endl;
    }
  }
}

C++: #include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <utility>
#include <functional>
#include <sstream>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <climits>
#include <cassert>
using namespace std;
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define REP(i,n) FOR(i,0,(n)-1)
const double EPS = 1e-10;
const double PI  = acos(-1.0);

char change(char a, char b) {
	switch(a) {
	case 'r':
		return (b == 'g' ? 'b' : 'g');
	case 'g':
		return (b == 'r' ? 'b' : 'r');
	case 'b':
		return (b == 'r' ? 'g' : 'r');
	}
}

bool ok(string s) {
	REP(i, s.size()-1) {
		if(s[i] != s[i+1]) {
			return false;
		}
	}
	return true;
}

struct state {
	string s;
	int t;
	state(string s, int t) : s(s), t(t) {};
};

int main() {
	string s;
	while(cin >> s, s != "0") {
		queue<state> Q;
		Q.push(state(s, 0));
		set<string> S;
		S.insert(s);		
		int ans = -1;
		while(!Q.empty()) {
			state st = Q.front();
			Q.pop();
			string cs = st.s;

			if(ok(cs)) {
				ans = st.t;
				break;
			}

			REP(i, cs.size()-1) {
				if(cs[i] != cs[i+1]) {
					string ns = cs;
					char a = cs[i];
					char b = cs[i+1];
					ns[i] = change(a, b);
					ns[i+1] = change(a, b);

					if(S.find(ns) == S.end()) {
						S.insert(ns);
						Q.push(state(ns, st.t+1));
					}
				}
			}
		}

		if(ans != -1) {
			cout << ans << endl;
		} else {
			cout << "NA" << endl;
		}
	}

	return 0;
}