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 <queue>
#include <map>
#include <string>
using namespace std;

int main(){
	string str,tmp,s;
	bool f;
	while(cin >> str){
		queue<string> que;
		map<string,int> m;
		if(str == "0") break;
		que.push(str);
		while(!que.empty()){
			f = true;
			s = tmp = que.front();
			que.pop();
			for(int i = 0;i < s.length()-1;++i){
				if(s[i] != s[i+1]) f = false; 
			}
			if(f) break;
			for(int i = 0;i < tmp.length()-1;++i){
				if(tmp[i] == 'r'){
					if(tmp[i+1] == 'b') tmp[i] = tmp[i+1] = 'g';
					else if(tmp[i+1] == 'g') tmp[i] = tmp[i+1] = 'b';
				}
				else if(tmp[i] == 'b'){
					if(tmp[i+1] == 'r') tmp[i] = tmp[i+1] = 'g';
					else if(tmp[i+1] == 'g') tmp[i] = tmp[i+1] = 'r';
				}
				else if(tmp[i] == 'g'){
					if(tmp[i+1] == 'r') tmp[i] = tmp[i+1] = 'b';
					else if(tmp[i+1] == 'b') tmp[i] = tmp[i+1] = 'r';
				}
				if(!m.count(tmp)) {
					que.push(tmp);
					m[tmp] = m[s] + 1;
				}
				tmp = s;
			}
		}
		if(f) cout << m[s] << endl;
		else cout << "NA" << endl;
		m.clear();
		while(!que.empty()) que.pop();
	}
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int main(){
  typedef pair<string,int>P;
  while(1){
    string str;
    map<string,int>maps;
    queue<P>que;
    int kaku=0;
    cin>>str;
    if(str[0]=='0')break;
     que.push(P(str,0));
     while(!que.empty()){
       P p=que.front();que.pop();
       string  now,turn;
       int cnt=1;
       int ans;
       now=p.first;
       turn=p.first;
       ans=p.second;
       //   cout<<now<<" "<<ans<<endl;
       if(maps[now]==1)continue;
       maps[now]=1;
       
       for(int i=0;i<str.size()-1;i++){
	 if(now[i]==now[i+1])cnt++;
       }
       if(cnt==str.size()){
	 cout<<ans<<endl;
	 kaku=1;
	 break;
       }
       for(int i=0;i<str.size()-1;i++){
	 if(now[i]=='b' && now[i+1]=='r' || now[i]=='r' && now[i+1]=='b'){
	   now[i]='g';now[i+1]='g';
	   que.push(P(now,ans+1));
	   now=turn;
	 }
	 if(now[i]=='r' && now[i+1]=='g' || now[i]=='g' && now[i+1]=='r'){
	   now[i]='b';now[i+1]='b';
	   que.push(P(now,ans+1));
	   now=turn;
	 }
	 if(now[i]=='b' && now[i+1]=='g' || now[i]=='g' && now[i+1]=='b'){
	   now[i]='r';now[i+1]='r';
	   que.push(P(now,ans+1));
	   now=turn;
	 }
       }
     }
     if(!kaku)cout<<"NA"<<endl;
  }   
}

C++: #include <iostream>
#include <queue>
#include <map>
#include <algorithm>
using namespace std;

int f(char a,char b){
	if( a == 'r' && b == 'g' ) return 'b';
	if( a == 'b' && b == 'r' ) return 'g';
	if( a == 'b' && b == 'g' ) return 'r';
	swap(a,b);
	if( a == 'r' && b == 'g' ) return 'b';
	if( a == 'b' && b == 'r' ) return 'g';
	if( a == 'b' && b == 'g' ) return 'r';
	return 0;
}

int main(){
	string s;
	while(cin >> s && s != "0" ){
		map<string,int> done;
		queue< pair<string,int> > Q;
		Q.push(make_pair(s,0));
		while(Q.size()){
			pair<string,int> q = Q.front(); Q.pop();
			if( done[q.first]++) continue;
			if( count(q.first.begin(),q.first.end(),q.first[0]) == q.first.size() ) {
				cout << q.second << endl;
				goto exit;
			}
			for(int i = 0 ; i < q.first.size() - 1 ; i++){
				if( f(q.first[i],q.first[i+1]) ){
					char c = f(q.first[i],q.first[i+1]);
					string next = q.first;
					next[i] = next[i+1] = c;
					Q.push(make_pair(next,q.second+1));
				}
			}
		}
		cout << "NA" << endl;
		exit:;
	}
}

C++: #include <iostream>
#include <queue>
#include <map>
#include <set>
using namespace std;
typedef pair<string, int> P;
int main() {
    string w;
    while (cin>>w) {
        if (w=="0") break;
        queue<P> que;
        que.push(P(w,0));
        int res=-1;
        set<string> done;
        while (!que.empty()) {
            P p=que.front(); que.pop();
            char f=p.first[0]; bool flag=true;
            for (int i=1; i<p.first.length(); i++) if (p.first[i]!=f) {
                flag=false;
                break;
            }
            if (flag) {
                res=p.second;
                break;
            }
            for (int i=0; i<p.first.length()-1; i++) {
                if (p.first[i]!=p.first[i+1]) {
                    string temp=p.first;
                    if (temp[i]!='r'&&temp[i+1]!='r') {
                        temp[i]='r'; temp[i+1]='r';
                    } else if (temp[i]!='g'&&temp[i+1]!='g') {
                        temp[i]='g'; temp[i+1]='g';
                    } else if (temp[i]!='b'&&temp[i+1]!='b') {
                        temp[i]='b'; temp[i+1]='b';
                    }
                    if (done.count(temp)==0) {
                        que.push(P(temp,p.second+1));
                        done.insert(temp);
                    }
                }
            }
        }
        if (res==-1) puts("NA");
        else printf("%d\n",res);
    }
}