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;

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));	//?????\??????????????¶????????\??????

	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;
}

C++: #include <iostream>
#include <string>
#include <queue>
#include <vector>
#include <set>

using namespace std;

typedef vector<int> vi;

inline bool ok(const vi & v){
    for (int i = 1; i < v.size(); i++){
        if (v[i] != v[0]) return false;
    }
    return true;
};

struct state {
    vi v;
    int n;
};

int main(){
    string s;
    while (cin >> s, s != "0"){
        vi init(s.size());
        for (int i = 0; i < s.size(); i++){
            if (s[i] == 'r') init[i] = 0;
            else if (s[i] == 'g') init[i] = 1;
            else init[i] = 2;
        }
        queue<state> q;
        set<vi> dp;
        q.push({ init, 0 });

        int ans = -1;
        while (q.size()){
            state sta = q.front();
            q.pop();
            vi & sv = sta.v;
            auto pr = dp.insert(sv);
            if (!pr.second){
                continue;
            }
            if (ok(sv)){
                ans = sta.n;
                break;
            }
            for (int i = 1; i < sv.size(); i++){
                if (sv[i] != sv[i - 1]){
                    int a = sv[i];
                    int b = sv[i - 1];
                    sv[i] = sv[i - 1] = 3 - (a + b);
                    q.push({ sv, sta.n + 1 });
                    sv[i] = a;
                    sv[i - 1] = b;
                }
            }
        }
        if (ans == -1){
            cout << "NA" << endl;
        }
        else{
            cout << ans << endl;
        }
    }
}

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

using namespace std;

typedef pair<string, int> P;

int main() {
	string s;
	while (cin >> s) {
		if (s == "0") {
			break;
		}
		map<string, int> mp;
		queue<P> q;
		q.push(P(s, 0));
		int count = -1;
		int sz = s.size();
		char cc = s[0];
		bool hantei = true;
		for (int i = 1; i < sz; i++) {
			if (s[i] != cc) {
				hantei = false;
				break;
			}
		}
		mp[s]++;
		if (hantei) {
			cout << 0 << endl; 
		} else {
			while (!q.empty()) {
				P aa = q.front();
				q.pop();
				string a = aa.first;
				for (int i = 0; i < sz-1; i++) {
					if (a[i] == a[i+1]) {
					} else {
						string b = a;
						if ((a[i] == 'r' && a[i+1] == 'g')||(a[i] == 'g' && a[i+1] == 'r')) {
							b[i] = b[i+1] = 'b';
						} else if ((a[i] == 'g' && a[i+1] == 'b')||(a[i] == 'b' && a[i+1] == 'g')) {
							b[i] = b[i+1] = 'r';
						} else {
							b[i] = b[i+1] = 'g';
						}
						//cout << b << endl;
						mp[b]++;
						if (mp[b] > 1) {
						} else {
							char ccb = b[0];
							bool hantei2 = true;
							for (int i = 1; i < sz; i++) {
								if (b[i] != ccb) {
									hantei2 = false;
									break;
								}
							}
							if (hantei2) {
								count = aa.second+1;
								break;
							} else {
								q.push(P(b, aa.second+1));
							}
						}
					}
				}
				if (count != -1) {
					break;
				}
			}
			if (count != -1) {
				cout << count << endl;
			} else {
				cout << "NA" << endl;
			}
		}
	}
	return 0;
}