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 <utility>
#include <vector>
#include <set>
#include <queue>
using namespace std;

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


char othercolor(char a, char b){
  if(a != b){
    if(a != 'r' && b != 'r'){ return 'r'; }
    if(a != 'g' && b != 'g'){ return 'g'; }
    if(a != 'b' && b != 'b'){ return 'b'; }
  }
  return -1;
}


int main(void){
  while(true){
    string initworm;
    cin >> initworm;
    if(initworm == "0"){ break; }

    queue<pair<int, string> > wait;
    set<string> used;
    wait.push(make_pair(0, initworm));
    used.insert(initworm);
    
    int ans = -1;
    while(!wait.empty()){
      int nowcost = wait.front().first;
      string nowworm = wait.front().second;
      wait.pop();

      if(terminal(nowworm)){
        ans = nowcost;
        break;
      }

      // ??£??\??¶???
      for(int i = 1; i < (int)nowworm.size(); i++){
        char c = othercolor(nowworm[i], nowworm[i - 1]);
        // ???????????????????????????????????§???????????????
        if(c != -1){
          string next = nowworm;
          next[i] = next[i - 1] = c;
          // ????????¶???????????¢?´¢?????£?????´???
          if(used.count(next) == 0){
            used.insert(next);
            wait.push(make_pair(nowcost + 1, next));
          } 
        }
      }      
    }
    
    // ??????
    if(ans == -1){ cout << "NA" << endl; }
    else{ cout << ans << endl; }
  }
  return 0;
}

C++: #include <iostream>
#include <string>
#include <queue>
#include <utility>
#include <set>
using namespace std;
typedef pair<string,int> P;
int main() {
	string S;
	while(cin>>S) {
		set<string> ST;
		queue<P> Q;
		Q.push(P(S,0));
		string R,G,B;
		bool OK;
		while(!Q.empty()) {
			P p=Q.front();Q.pop();
			OK=true;
			for(int i=0;i<p.first.size()-1;i++) {
				string SS=p.first;
				if((p.first[i]=='r'&&p.first[i+1]=='g')||(p.first[i]=='g'&&p.first[i+1]=='r')) {
						SS[i]=SS[i+1]='b';
						if(ST.find(SS)==ST.end()){
							Q.push(P(SS,p.second+1));
							ST.insert(SS);
						}
						OK=false;
				}else if((p.first[i]=='r'&&p.first[i+1]=='b')||(p.first[i]=='b'&&p.first[i+1]=='r')) {
						SS[i]=SS[i+1]='g';
						if(ST.find(SS)==ST.end()){
							Q.push(P(SS,p.second+1));
							ST.insert(SS);
						}
						OK=false;
				}else if((p.first[i]=='g'&&p.first[i+1]=='b')||(p.first[i]=='b'&&p.first[i+1]=='g')) {
						SS[i]=SS[i+1]='r';
						if(ST.find(SS)==ST.end()){
							Q.push(P(SS,p.second+1));
							ST.insert(SS);
						}
						OK=false;
				}
			}
			if(OK) {printf("%d\n",p.second);break;}
		}
		if(!OK)printf("NA\n");
	}
}

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

using namespace std;

typedef pair <string, int> P;

#define mp(a, b) make_pair(a, b)

char diff(char a, char b)
{
	if (a != 'r' && b != 'r') return 'r';
	if (a != 'g' && b != 'g') return 'g';
	if (a != 'b' && b != 'b') return 'b';
	return 'a';
}

bool check(string str)
{
	char c = str[0];
	for (int i = 0; i < str.length(); i++){
		if (c != str[i]) return false;
	}

	return true;
}

int main(void)
{
	string str;

	while (cin >> str){
		if (str == "0") return 0;

		int ret = -1, a;
		queue < P > q;
		q.push(mp(str, 0));
		while (!q.empty()){
			P now = q.front();
			q.pop();
			if (check(now.first)){
				ret = now.second;
				break;
			}
			if (q.size() > 1e6){
				break;
			}
			for (int i = 0; i < now.first.length()-1; i++){
				if (now.first[i] != now.first[i + 1]){
					string tmp = now.first;
					tmp[i] = diff(now.first[i], now.first[i + 1]);
					tmp[i + 1] = diff(now.first[i], now.first[i + 1]);
					q.push(mp(tmp, now.second + 1));
				}
			}
		}

		if (ret >= 0) cout << ret << endl;
		else cout << "NA" << endl;
	}

	return 0;
}