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>
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 <cstdio>
#include <cstdlib>
#include <string>
#include <vector>
#include <deque>
#include <list>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <cstring>
#include <cctype>
#include <sstream>
#include <set>
#include <map>
#include <queue>
#include <complex>
using namespace std;

int main() {
  string musi;
  while(cin >> musi, musi != "0") {
    string tonum;
    for(int i=0; i<musi.size(); i++) {
      if(musi[i] == 'r')
        tonum.push_back('1');
      if(musi[i] == 'g')
        tonum.push_back('2');
      if(musi[i] == 'b')
        tonum.push_back('3');
    }
    queue< pair<string, int> > q;
    pair<string, int> p;
    p.first = tonum;
    p.second = 0;
    q.push(p);
    bool flg = true;
    set<string> memo;
    int test = 0;
    while(q.size()) {
      p = q.front();
      q.pop();
      int cnt = 0;
      for(int i=1; i<p.first.size(); i++) {
        if(p.first[i-1] != p.first[i]) {
          pair<string, int> p2;
          p2 = p;
          int n = (int)p.first[i-1] + (int)p.first[i] - '0' - '0';
          if(n==3) {
            p2.first[i-1] = '3';
            p2.first[i] = '3';
          }
          else if(n==4) {
            p2.first[i-1] = '2';
            p2.first[i] = '2';
          }
          else if(n==5) {
            p2.first[i-1] = '1';
            p2.first[i] = '1';
          }
          if(memo.find(p2.first) == memo.end()) {
            p2.second++;
            q.push(p2);
            memo.insert(p2.first);
          }
        }
        else cnt++;
      }
      if(cnt == p.first.size()-1) {
        flg = false;
        cout << p.second << endl;
        break;
      }
    }
    if(flg) cout << "NA" << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using P = pair<string, int>;

int main() {
  map<char, int> rbg;
  rbg['r'] = 0;
  rbg['b'] = 1;
  rbg['g'] = 2;

  string s;
  while (cin >> s && s[0] != '0') {
    int len = s.length();
    vector<string> goal(3);
    for (int i = 0; i < 3; ++i) {
      goal[i] = string(len, "rbg"[i]);
    }

    auto check = [&](string s) {
      for (int i = 0; i < 3; ++i) {
        if (goal[i] == s) return true;
      }
      return false;
    };
    int ans;
    bool ok = true;
    queue<P, deque<P>> que;
    map<string, bool> mp = {{s, true}};

    que.push({s, 0});
    while (ok) {
      tie(s, ans) = que.front(); que.pop();
      if (check(s)) break;

      for (int i = 0; i < len - 1; ++i) {
        if (s[i] == s[i + 1]) continue;
        string nxt = s;
        int n = 3 - rbg[s[i]] - rbg[s[i + 1]];
        nxt[i] = nxt[i + 1] = "rbg"[n];
        if (!mp[nxt]) {
          que.push({nxt, ans + 1});
          mp[nxt] = true;
        }
      }
      if (que.empty()) ok = false;
    }
    cout << ( (ok) ? to_string(ans) : "NA" ) << endl;
  }
  return 0;
}