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>
#include <algorithm>
using namespace std;

int cnt,ccnt = 0;
int len;
string s, ss, tmp;
int flag = 0;
int fflag=0;
char c;
vector<string> v_list;
pair<string,int> ps;
int main() {
	while (cin >> s) {
		if (s == "0") {
			break;
		}
		fflag=0;
		//v_list.push_back(s);
		len = s.length();
		queue<pair<string,int> > qq;
		qq.push(make_pair(s,0));
		while (!qq.empty()) {
			ps = qq.front();
			qq.pop();
			c = ps.first[0];

			ccnt=ps.second;
			flag = 0;
			//vector<int>::iterator cIter = std::find( v_list.begin(), v_list.end(), ps.first);

			/*if( (find( v_list.begin(), v_list.end(), ps.first)) != v_list.end() ){
				continue;
			}
			v_list.push_back(ps.first);*/

			for (int i = 1; i < len; i++) {
				if (c != ps.first[i]) {
					//cout<<ps.first[i]<<endl;//deb
					flag = 1;
					break;
				}
			}
			if (flag) {
				for (int i = 0; i < len - 1; ++i) {
					tmp = ps.first;
					if (ps.first[i] != ps.first[i+1]) {
						if (ps.first[i] != 'r' && ps.first[i+1] != 'r') {
							tmp[i] = 'r';
							tmp[i + 1] = 'r';
							//cout<<tmp<<endl;//deb
							if( (find( v_list.begin(), v_list.end(), tmp)) != v_list.end() ){
								continue;
							}
							v_list.push_back(tmp);

							qq.push(make_pair(tmp,ccnt+1));
						}
						if (ps.first[i] != 'g' && ps.first[i+1] != 'g' ){
							tmp[i] = 'g';
							tmp[i + 1] = 'g';
							//cout<<tmp<<endl;//deb
							if( (find( v_list.begin(), v_list.end(), tmp)) != v_list.end() ){
									continue;
							}
							v_list.push_back(tmp);
							qq.push(make_pair(tmp,ccnt+1));
						}
						if (ps.first[i] != 'b' && ps.first[i+1] != 'b') {
							tmp[i] = 'b';
							tmp[i + 1] = 'b';
							//cout<<tmp<<endl;//deb
							if( (find( v_list.begin(), v_list.end(), tmp)) != v_list.end() ){
									continue;
							}
							v_list.push_back(tmp);
							qq.push(make_pair(tmp,ccnt+1));
						}
					}
				}
			} else {
				cout << ccnt << endl;
				fflag=1;
				break;
			}
		}
		if(!fflag){printf("NA");cout<<endl;};
	}
	return 0;
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
#include<math.h>
#include<map>
#include<queue>

using namespace std;

string InputStr, StrNow;
map<string, int> DpResult;


bool isAllSame() {
	int size;

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

bool solve() {
	int size;
	string strPrev;
	queue<string> CurrentStr;

	DpResult[InputStr] = 0;
	CurrentStr.push(InputStr);

	while (!CurrentStr.empty()) {
		StrNow = strPrev = CurrentStr.front();
		CurrentStr.pop();

		//cout << "befor:" << strPrev << endl;
		size = StrNow.size() - 1;
		for (int i = 0; i < size; i++) {
			StrNow = strPrev;
			if ((StrNow[i] == 'r' && StrNow[i + 1] == 'g') || (StrNow[i] == 'g' && StrNow[i + 1] == 'r')) {
				StrNow[i] = StrNow[i + 1] = 'b';
			}
			else if ((StrNow[i] == 'r' && StrNow[i + 1] == 'b') || (StrNow[i] == 'b' && StrNow[i + 1] == 'r')) {
				StrNow[i] = StrNow[i + 1] = 'g';
			}
			else if ((StrNow[i] == 'g' && StrNow[i + 1] == 'b') || (StrNow[i] == 'b' && StrNow[i + 1] == 'g')) {
				StrNow[i] = StrNow[i + 1] = 'r';
			}

			//cout << "after:" << StrNow << endl;
			if (DpResult.find(StrNow) == DpResult.end()) {
				CurrentStr.push(StrNow);
				DpResult[StrNow] = DpResult[strPrev] + 1;
			}

			if (isAllSame()) {
				return true;
			}
		}
	}

	return false;
}

int main() {

	while (cin >> InputStr, InputStr[0] != '0') {
		//cout << InputStr << endl;
		DpResult.clear();		
		if (solve()) {
			cout << DpResult[StrNow] << endl;
		}
		else {
			cout << "NA" << endl;
		}
	}

	return 0;
}