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 <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() > 800000){
				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;
}

C++: #include <iostream>
#include <queue>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <map>
#include <string>
using namespace std;

const int INF = 1e+9;
typedef pair<int, int> P;

int ans = 0;
int s_size;

string change(string s, int a, int b){
	if((s[a] == 'r' && s[b] == 'g') || (s[a] == 'g' && s[b] == 'r'))
		s[b] = s[a] = 'b';
	else if((s[a] == 'b' && s[b] == 'g') || (s[a] == 'g' && s[b] == 'b'))
		s[b] = s[a] = 'r';
	else
		s[b] = s[a] = 'g';
	
	return s;
}

void bfs(string s, int res){
	if(res >= ans)
		return;
	for(int i = 0; i < s_size - 1; ++i){
		if(s[i] != s[i + 1])
			break;
		if(i == s_size - 2){
			ans = min(res, ans);
			return;
		}
	}
	if(res >= s_size)
		return;
	for(int i = 0; i < s_size - 1; ++i){
		if(s[i] != s[i + 1]){
			string str = change(s, i, i + 1);
			bfs(str, res + 1);
		}
	}
}

int main() {
	std::ios::sync_with_stdio(false);
    std::cin.tie(0);
	string s;
	while(cin >> s){
		if(s == "0")
			break;
		s_size = s.size();
		ans = INF;
		bfs(s, 0);
		if(ans == INF)
			cout << "NA" << endl;
		else
			cout << ans << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <string>
#include <map>
#include <queue>
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 = false;
		for(int i=0;i<str.size()-1;i++){
			if(str[i] != str[i+1]){
				flag = true;
				break;
			}
		}

		if(!flag) return p.second;

		d[p.first] = p.second;

		for(int i=0;i<str.size()-1;i++){
			if(str[i] != str[i+1]){
				char temp;
				string next;

				if(str[i] != 'b' && str[i+1] != 'b'){
					temp = 'b';
				}else if(str[i] != 'g' && str[i+1] != 'g'){
					temp = 'g';
				}else{
					temp = 'r';
				}

				next = str;
				next[i] = next[i+1] = temp;

				que.push(P(next, p.second+1));
			}
		}
	}
	return -1;
}

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

C++: #include <bits/stdc++.h>

using namespace std;

typedef pair<string, int> P;

//????????????????????????????????????
bool judge(string str) {
	for (int i = 0; i < str.size(); ++i) {
		if (str[0] != str[i]) return false;
	}
	return true;
}

//??£?????????2?????????????????§?????????????????????
char color(char a, char b){
	if((a == 'g' && b == 'r') || (a == 'r' && b == 'g'))return 'b';
	else if((a == 'b' && b == 'r') || (a == 'r' && b == 'b')) return 'g';
	else if((a == 'g' && b == 'b') || (a == 'b' && b == 'g')) return 'r';
}

int solve(string s ){

	queue<P> q;
	map<string, int> m;
	q.push(P(s, 0));	//?????\??????????????¶????????\??????
	if(m[p.first]) continue;

	while (!q.empty()) {	//?????\??????????????¶?????????????????§
		P p = q.front();
		q.pop();
		string now = p.first;
		if (judge(now)) return p.second;
		for (int i = 0; i < now.size() - 1; ++i) {
			if (now[i] != now[i+1]){	//??£?????????2????????°????????¨???
				char tmp = color(now[i], now[i + 1]);
				string D = now;
				D[i] = tmp;
				D[i + 1] = tmp;
				q.push(P(D, p.second + 1));
			}
		}
	}
	return -1;
}

int main() {
	string worm;
	while (cin >> worm) {
		if (worm == "0") break;
		int count = solve(worm);
		if (count == -1) cout << "NA" << endl;
		else cout << count << endl;
	}
	return 0;
}