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>

#define FOR(i, n, m) for(int i = (n);i < (m);i++)
#define REP(i, n) for(int i = 0;i < (n);i++)
#define PII pair<int, int>

using namespace std;

string worm;

int all(string a){
    char b = a[0];
    int cnt = 0;
    for(int i = 1;a[i] != '\0';i++){
        if(a[i] != b)
            cnt++;
    }
    return cnt;
}

int solve(){
    queue< pair<string, int> > que;
    que.push(pair<string, int>(worm, 0));
    string worm1, tmp;
    int num;

    if(all(worm) == 0){
        return 0;
    }

    while(que.size()){
        worm1 = que.front().first;
        num = que.front().second;
        que.pop();

        if(all(worm1) == 1){
            continue;
        }else if(all(worm1) == 0){
            return num;
        }

        if(num >= 10){
            return -1;
        }
        for(int i = 0;i < strlen(worm1.c_str())-1;i++){
            tmp = worm1;
            if(worm1[i] != worm1[i+1]){
                if((worm1[i] == 'b' && worm1[i+1] == 'g') || (worm1[i] == 'g' && worm1[i+1] == 'b')){
                    tmp[i] = tmp[i+1] = 'r';
                    que.push(pair<string, int>(tmp, num+1));
                }else if((worm1[i] == 'b' && worm1[i+1] == 'r') || (worm1[i] == 'r' && worm1[i+1] == 'b')){
                    tmp[i] = tmp[i+1] = 'g';
                    que.push(pair<string, int>(tmp, num+1));
                }else{
                    tmp[i] = tmp[i+1] = 'b';
                    que.push(pair<string, int> (tmp, num+1));
                }
            }
        }
    }

    return -1;
}

int main(void){
    cin >> worm;
    while(worm[0] != '0'){
        int result = solve();
        if(result >= 0){
            cout << result << endl;
        }else{
            cout << "NA" << endl;
        }
        cin >> worm;
    }

    return 0;
}

C++: #include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
const ld eps = 1e-9;

//// < "d:\d_download\visual studio 2015\projects\programing_contest_c++\debug\a.txt" > "d:\d_download\visual studio 2015\projects\programing_contest_c++\debug\b.txt"


map<char, int>chmp;

int main() {
	chmp['r'] = 0;
	chmp['g'] = 1;
	chmp['b'] = 2;
	while (1) {

		string st; cin >> st;
		if (st == "0")break;
		vector<int>nums;
		for (auto c : st) {
			nums.emplace_back(chmp[c]);
		}

		map<vector<int>, int>mp;
		queue<pair<int,vector<int>>>que;
		que.push(make_pair(0,nums));
		int ans = 1e8;
		while (!que.empty()) {
			auto p(que.front());
			que.pop();
			if (mp.find(p.second) != mp.end())continue;
			mp[p.second];
			if (all_of(p.second.begin(), p.second.end(), [=](const int n) {return n == p.second[0]; })) {
				ans = p.first;
				break;
			}
			vector<int>st(p.second);
			for (int i = 0; i < st.size() - 1; ++i) {
				if (st[i] != st[i + 1]) {
					vector<int>nowst(st);
					nowst[i] = 3 - st[i] - st[i + 1];
					nowst[i + 1] = 3 - st[i] - st[i + 1];
					que.push(make_pair(p.first + 1, nowst));
				}
			}
		}
		if (ans > 1e7) {
			cout << "NA" << endl;
		}
		else {
			cout << ans << endl;
		}
	}
	return 0;
}

C++: #include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<queue>
#include<map>
using namespace std;
struct data{
	string str;
	int cnt;
	data(){}
	data(string str,int cnt):str(str),cnt(cnt){}
};
string func(string str,int i) {
	int r,g,b;
	char change;
	if(str[i] == 'r') {
		if(str[i+1] == 'g') change='b';
		else if(str[i+1] == 'b') change = 'g';
		else return str;
	}
	else if(str[i] == 'g') {
		if(str[i+1] == 'r') change='b';
		else if(str[i+1] == 'b') change = 'r';
		else return str;
	}
	else {
		if(str[i+1] == 'g') change = 'r';
		else if(str[i+1] == 'r') change = 'g';
		else return str;
	}
	str[i] = change;
	str[i+1] = change;
	return str;
}
bool check(string str) {
	char c = str[0];
	for(int i = 0; i < str.size(); i++) {
		if(str[i] != c) return false;
	}
	return true;
}
map<string,int> memo;
int main() {
	string str;
	while(1) {
		cin >> str;
		if(str == "0") break;
		int ans = -1;
		queue<data> Q;
		Q.push(data(str,0));
		while(!Q.empty()) {
			data d = Q.front();Q.pop();
			if(memo.find(d.str) != memo.end()) continue;
			memo[d.str] = d.cnt;
			if(check(d.str)) {
				ans = d.cnt;
				break;
			}
			for(int i = 0; i < d.str.size() - 1; i++) {
				string nstr = func(d.str,i);
				if(nstr == d.str) continue;
				Q.push(data(nstr,d.cnt+1));
			}
		}
		if(ans == -1) puts("NA");
		else printf("%d\n",ans);
	}
	return 0;
}