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 <map>
using namespace std;

map<string, int> seenbefore;
string in;
map<string, int>::iterator it;

string check(string twochars){
  if(twochars[0] == twochars[1]) return "";
  if(twochars[0] == 'r')
    if(twochars[1] == 'g') return "b";
    else return "g";
  else
    if(twochars[0] == 'g')
      if(twochars[1] == 'r') return "b";
      else return "r";
    else
      if(twochars[1] == 'r') return "g";
      else return "r";
}

int next_generation(string now, int gen){
  if(now.find("r") + now.find("g") + now.find("b") == -2) return gen;
  if((it = seenbefore.find(now)) != seenbefore.end()){
    if((*it).second > gen) (*it).second = gen;
    else return -1;
  }
  seenbefore.insert(map<string, int>::value_type(now, gen));
  int len = now.length();
  int ans = 99999999, y;
  for(int i = 0; i < len - 1; i++){
    string che = check(now.substr(i, 2));
    if(che != ""){
      y = next_generation(now.substr(0, i) + che + che + now.substr(i+2), gen + 1);
      if(y != -1) ans = min(ans, y);
    }
  }
  return ans;
}

int main(){
  while((cin >> in), in != "0"){
    seenbefore.clear();
    int x = next_generation(in, 0);
    if (x >= 0) cout << x << endl;
    else cout << "NA" << endl;
  }
  return 0;
}

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

using namespace std;

map<string,bool > passed;
map<string,int> dp;

const int INF=100000000;

int dfs(string str){
	if(dp.find(str)!=dp.end()){
		return dp[str];
	}
	if(passed.find(str)!=passed.end()&&passed[str]){
		return INF;
	}
	char cl=str[0];
	bool f=false;
	for(int i = 1; i < str.size(); i++){
		if(str[i]!=cl){
			f=true;
			break;
		}
	}
	if(!f)
		return 0;

	bool flag[200];
	int minCnt=INF;
	for(int i = 0; i < str.size()-1; i++){
		flag['r']=false;
		flag['g']=false;
		flag['b']=false;
		if(str[i]!=str[i+1]){
			flag[str[i]]=true;
			flag[str[i+1]]=true;
			if(!flag['r']){
				string nstr=str;
				nstr[i]='r';
				nstr[i+1]='r';
				passed[str]=true;
				minCnt=min(minCnt,dfs(nstr)+1);
				passed[str]=false;
			}
			else if(!flag['g']){
				string nstr=str;
				nstr[i]='g';
				nstr[i+1]='g';
				passed[str]=true;
				minCnt=min(minCnt,dfs(nstr)+1);
				passed[str]=false;
			}
			else if(!flag['b']){
				string nstr=str;
				nstr[i]='b';
				nstr[i+1]='b';
				passed[str]=true;
				minCnt=min(minCnt,dfs(nstr)+1);
				passed[str]=false;
			}
		}
	}
	//if(minCnt!=INF)
		dp[str]=minCnt;
	return minCnt;
}

int main(){

	string str;
	while(cin>>str&&str!="0"){
		dp.clear();
		passed.clear();
		int ret=dfs(str);
		if(ret!=INF)
			cout<<ret<<endl;
		else
			cout<<"NA"<<endl;
	}


	return 0;
}

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

typedef pair<string,int> P;
typedef map<string,int> M;

int dfs(string str) {
     queue<P> s;
     s.push(P(str,0));
     int res = 999999999;
     bool f2 = true;
     M m;

     while (s.size()) {
	  P p = s.front(); s.pop();
	  str = p.first;
	  if (m[str]) continue;
	  int num = p.second;
	  m[str] = num;
	  bool f = true;
	  int count = 0;
	  for (int i = 0; i < str.size() - 1; i++) {
	       string tmp = str;
	       bool flag = false;
	       if (tmp[i] != tmp[i + 1]) {
		    flag = true;
		    f = false;
		    count++;
		    if (tmp[i] != 'b' && tmp[i + 1] != 'b')
			 tmp[i + 1] = tmp[i] = 'b';
		    else if (tmp[i] != 'r' && tmp[i + 1] != 'r')
			 tmp[i + 1] = tmp[i] = 'r';
		    else if (tmp[i] != 'g' && tmp[i + 1] != 'g')
			 tmp[i + 1] = tmp[i] = 'g';
		    if (tmp == str) flag = false;
	       }
	       if (flag && res > num + 1) s.push(P(tmp, num + 1));
	  }
	  if (f && res > num) {
	       res = num;
	       f2 = false;
	       break;
	  }
	  if (count == 1) s.pop();
     }
     if (f2) res = -1;
     return res;
}

int main()
{
     string str;
     while (cin >> str) {
	  if (str == "0") break;
	  int res = dfs(str);
	  if (res < 0) cout << "NA" << endl;
	  else cout << res << endl;
     }


     return 0;
}