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<cstdio>
#include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
struct s{
    string worm;
    int nowans;
};
int main(){
    char dc[6][3]={'r','g','b','g','r','b','r','b','g','b','r','g','g','b','r','b','g','r'};
    while(1){
        s IN,now;
        queue 
 que;
        cin >> IN.worm;
        IN.nowans=0;
        if(IN.worm[0]=='0')
            break;
        que.push(IN);
        while(1){
            now=que.front(),que.pop();
            for(int i=0;i<now.worm.size()-1;i++){
                if(now.worm[i]!=now.worm[i+1])
                    break;
                if(i==now.worm.size()-1-1){
                    printf("%d\n",now.nowans);
                    goto exit;
                }
            }
            if(now.nowans==10){
                puts("NA");
                goto exit;
            }
            for(int i=0;i<now.worm.size()-1;i++){
                if(now.worm[i]!=now.worm[i+1]){
                    for(int j=0;j<6;j++){
                        if(now.worm[i]==dc[j][0]&&now.worm[i+1]==dc[j][1]){
                            now.worm[i]=dc[j][2],now.worm[i+1]=dc[j][2],now.nowans++;
                            que.push(now);
                            now.worm[i]=dc[j][0],now.worm[i+1]=dc[j][1],now.nowans--;
                        }
                    }
                }
            }
        }
exit:
    printf("");
    }
    return 0;
}

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

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

using namespace std;

char get_color(char c1, char c2) {
    if ((c1 == 'r' && c2 == 'g') || (c1 == 'g' && c2 == 'r'))
        return 'b';
    else if ((c1 == 'g' && c2 == 'b') || (c1 == 'b' && c2 == 'g'))
        return 'r';
    else
        return 'g';
}

bool is_finish(string s) {
    rep(i, s.size()) if (s[0] != s[i]) return false;
    return true;
}

string s;
void solve() {
    queue<string> worm;
    map<string, int> dict;

    int ans = -1;
    worm.push(s);
    while (worm.size()) {
        string t = worm.front();
        int now = dict[t];
        worm.pop();
        if (is_finish(t)) {
            ans = now;
            break;
        }

        rep(i, t.size() - 1) {
            if (t[i] != t[i + 1]) {
                string next = t;
                next[i] = next[i + 1] = get_color(t[i], t[i + 1]);
                if (dict.count(next) == 0) {
                    // cout << t << " -> " << next << endl;
                    worm.push(next);
                    dict[next] = now + 1;
                }
            }
        }
    }
    if(ans == -1) cout << "NA" << endl;
    else cout << ans << endl;
}

int main() {
    while (cin >> s) {
        if (s == "0") break;
        solve();
    }
}

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

using namespace std;

bool Check_Warm_Color(string str) {
	char c = str[0];
	for (int i = 1; i < str.length(); ++i) {
		if (c != str[i]) {
			return false;
		}
	}
	return true;
}

char Check_Color(char c1, char c2) {
	if (c1 < c2) {
		swap(c1,c2);
	}
	if (c1 == 'r') {
		if (c2 == 'g') {
			return 'b'; 
		}
		else {
			return 'g';
		}
	}
	return 'r';
}

int main(void) {
	string str,ss;
	cin >> str;
	while (str != "0") {
		int len = str.length();
		map<string,bool> ob;
		ob[str] = true;

		queue<string> warm;
		queue<int> deep;
		warm.push(str);
		deep.push(0);
		bool find = false;
		int d;
		int ret = -1;
		while (!find && !warm.empty()) {
			str = warm.front();
			d = deep.front();
			warm.pop();
			deep.pop();
			if (Check_Warm_Color(str)) {
				ret = d;
				find = true;
			}
			else {
				for (int i = 0; i < str.length() - 1; ++i) {
					ss = str;
					if (str[i] != str[i+1]) {
						char temp = Check_Color(str[i],str[i+1]);
						ss[i] = temp;
						ss[i+1] = temp;
					}
					if (!ob[ss]) {
						ob[ss] = true;
						warm.push(ss);
						deep.push(d+1);
					}
				}
			}
		}
		if (ret < 0) {
			cout << "NA" << endl;
		}
		else {
			cout << ret << endl;
		}

		cin >> str;
	}
	return 0;
}