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 <vector>
#include <algorithm>
#include <queue>
#include <map>

#define REP(i,k,n) for(int i=k;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)

using namespace std;

struct W
{
	string s;
	int num;
	
	W(string s = "",int num = 0) : s(s),num(num) {}
};

char change(char a,char b)
{
	if((a == 'r' && b == 'g') || (a == 'g' && b == 'r'))
	{
		return 'b';	
	}
	else if((a == 'r' && b == 'b') || (a == 'b' && b == 'r'))
	{
		return 'g';
	}
	else if((a == 'g' && b == 'b') || (a == 'b' && b == 'g'))
	{
		return 'r';
	}
	return 'N';
}

int main()
{
	string s;
	while(cin >> s)
	{
		if(s == "0") break;
		
		string t = "",t2 = "",t3 = "";
		rep(i,s.size())
		{
			t += "r";
			t2 += "g";
			t3 += "b";
		}

		queue<W> que;
		que.push(W(s,0));
		map<string,int> m;
		int ans = 0;
		bool flag = true;

		while(!que.empty())
		{
			W w = que.front();
			que.pop();

			if(m[w.s] > 0) 
			{
				continue;
			}

			if(w.s == t || w.s == t2 || w.s == t3)
			{
				flag = false;
				ans = w.num;
				break;
			}

			m[w.s] = w.num;

			rep(i,s.size()-1)
			{
				string temp = w.s;
				if(change(w.s[i],w.s[i+1]) == 'N') continue;
				
				temp[i] = temp[i+1] = change(w.s[i],w.s[i+1]);
				que.push(W(temp,w.num+1));
			}
		}
		if(flag) cout << "NA" << endl;
		else cout << ans << endl;
	}

	return 0;
}

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

using namespace std;

typedef pair<string, int> P;

char keisan(char a, char b) {
	if (a == b) {
		return a;
	} else {
		string abc = "rbg";
		int aa, bb;
		for (int i = 0; i < 3; i++) {
			if (a == abc[i]) {
				aa = i;
			} 
			if (b == abc[i]) {
				bb = i;
			}
		}
		return abc[3-(aa+bb)];
	}
}

bool hantei(string a) {
	for (int i = 1; i < a.size(); i++) {
		if (a[0] != a[i]) {
			return false;
		}
	}
	return true;
}

int main() {
	string a;
	while (cin >> a) {
		if (a[0] == '0') {
			break;
		}
		if (hantei(a)) {
			cout << 0 << endl;
		} else {
			queue<P> q;
			vector<string> hyou;
			hyou.push_back(a);
			bool hantei2 = false;
			for (int i = 0; i < a.size()-1; i++) {
				string c;
				c = a;
				c[i] = keisan(a[i], a[i+1]);
				c[i+1] = keisan(a[i], a[i+1]);
				if (hantei(c)) {
					cout << 1 << endl;
					hantei2 = true;
					break;
				} else {
					P p;
					p.first = c;
					p.second = 2;
					q.push(p);
					hyou.push_back(c);
				}
			}
			while (!q.empty()) {
				if (hantei2) {
					break;
				}
				P p = q.front();
				q.pop();
				string b = p.first;
				for (int i = 0; i < b.size()-1; i++) {
					string c;
					c = b;
					c[i] = keisan(b[i], b[i+1]);
					c[i+1] = keisan(b[i], b[i+1]);
					if (hantei(c)) {
						cout << p.second << endl;
						hantei2 = true;
						break;
					} else {
						bool hantei3 = true;
						for (int i = 0; i < hyou.size(); i++) {
							if (c == hyou[i]) {
								hantei3 = false;
								break;
							}
						}
						if (hantei3) {
							P pp;
							pp.first = c;
							pp.second = p.second+1;
							q.push(pp);
							hyou.push_back(c);
						}
					}
				}
			}
			if (!hantei2) {
				cout << "NA" << endl;
			}
		}
	}
	return 0;
}