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

typedef pair<string,bool> P;

int main()
{

  string worm;

  while(cin >> worm && worm != "0")
    {

      map<string,bool> state_record;
      queue<string> worm_state;
      bool NAflag = false;
      bool flag = false;
      int rank = 0;

      worm_state.push(worm);

      while(!flag && !NAflag)
        {

          string temp;
          int state_num = worm_state.size();
          int count = 0;

          NAflag = true;

          for(int j = 0; j < state_num && !flag;j++)
            {

              if(state_record[worm_state.front()] == true)
                {
                  worm_state.pop();
                  continue;
                }
              for(int i = 0; i < worm.length() - 1 && !flag; i++)
                {

                  temp = worm_state.front();

                  if(!temp.compare(i, 2, "rg") || !temp.compare( i, 2, "gr"))
                    {
                      temp.replace(i,2,"bb");
                      worm_state.push(temp);
                    }
                  else if(!temp.compare(i, 2, "rb") || !temp.compare(i, 2, "br"))
                    {
                      temp.replace(i,2,"gg");
                      worm_state.push(temp);
                    }
                  else if(!temp.compare(i, 2, "gb") || !temp.compare(i, 2, "bg"))
                    {
                      temp.replace(i,2,"rr");
                      worm_state.push(temp);
                    }

                  count = 0;

                  for(int t = 0; t < worm.length(); t++) if(temp[0]==temp[t]) count++;

                  if(count == worm.length()) flag = true;

                }

              state_record[worm_state.front()] = true;

              worm_state.pop();

              NAflag = false;

            }

          if(!worm_state.empty()) rank++;

          if(flag) cout << rank << endl;

          if(NAflag) cout << "NA" << endl;

        }

      state_record.clear();

    }

  return 0;

}

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

using namespace std;
typedef pair<string, int> bug;
typedef map<string, int> closeMap;

int isOK(string str) {
    // cout << "str:" << str << " " << str.size() << endl;
    for ( int i = 0; i < str.size(); i++ ) {
        if ( str[0] != str[i] ) return 0;
    }
    return 1;
}

char cc(char a, char b) {
    // 並び替え
    if ( b < a ) {
        char tmp = a;
        a = b;
        b = tmp;
    }

    if ( a == 'b' && b == 'g' ) {
        return 'r';
    } else if ( a == 'b' && b == 'r' ) {
        return 'g';
    } else {
        return 'b';
    }
}

void wfs(string str) {
    int cnt = -1;
    string first = str;
    queue<bug> open;
    closeMap close;

    // 初期状態をプッシュ
    open.push( make_pair(str, 0) );

    close.insert( closeMap::value_type(str, 1) );
    // cout << str << " key:" << close[str] << endl;

    while(!open.empty()) {
        bug b = open.front(); open.pop();
        string cs = b.first;

        if ( isOK(cs) ) {
            cnt = b.second;
            break;
        }

        int c = 0;
        for ( int i = 1; i < cs.size(); i++ ) {
            if ( cs[i-1] != cs[i] ) {
                string tmp = cs;
                char nc = cc(cs[i-1], cs[i]);
                tmp[i-1] = nc;
                tmp[i] = nc;

                if ( close[tmp] )continue;
                open.push( make_pair(tmp, b.second+1) );
                close[tmp] = 1;
                c++;
            }
        }
    }

    if ( cnt == -1 ) {
        cout << "NA" << endl;
    } else {
        cout << cnt << endl;
    }


}

int main() {
    string n;

    while ( cin >> n, n != "0" ) {
        wfs(n);
    }

    return 0;
}

C++: #include<iostream>
#include<queue>
#include<map>
#include<cstdio>
using namespace std;
int main(){
	string s,t;for(int i,n,f;cin>>s,s!="0";){
		queue<string>q;
		map<string,int>d;d[s]=1;
		for(q.push(s);q.size();){
			s=q.front();q.pop();n=s.length();
			for(f=i=0;i<n-1;i++)if(s[i]!=s[i+1]){
				t=s;t[i]=t[i+1]=(char)('r'+'g'+'b'-s[i]-s[i+1]);f++;
				if(!d[t])d[t]=d[s]+1,q.push(t);
			}
			if(!f){printf("%d\n",d[s]-1);goto N;}
		}
		puts("NA");N:;
	}
}