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 <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;

bool check(string s) {
  for (int i = 0; i < int(s.size()); i++) {
    if (s[i] != s[0]) return false;
  }
  return true;
}

int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  
  const string col = "rgb";
  string s;
  while (cin >> s, s != "0") {
    int n = s.size();
    map<string, int> dis;
    queue<string> que;
    dis[s] = 0;
    que.emplace(s);
    int ans = -1;
    while (!que.empty()) {
      s = que.front(); que.pop();
      if (check(s)) {
        ans = dis[s];
        break;
      }
      for (int i = 0; i + 1 < n; i++) {
        if (s[i] == s[i + 1]) continue;
        for (int j = 0; j < 3; j++) {
          if (s[i] != col[j] && s[i + 1] != col[j]) {
            string ns = s;
            ns[i] = ns[i + 1] = col[j];
            if (dis.find(ns) != dis.end()) continue;
            dis[ns] = dis[s] + 1;
            que.emplace(ns);
          }
        }
      }
    }
    if (ans < 0) cout << "NA" << endl;
    else cout << ans << endl;
  }

  return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef pair<string, int> P;

bool judge(string str) {
	for (int i = 0; i < str.size(); ++i) {
		if (str[0] != str[i]) return false;
	}
	return true;
}

char color(char a, char b){
	if((a == 'g' && b == 'r') || (a == 'r' && b == 'g'))return 'b';
	else if((a == 'b' && b == 'r') || (a == 'r' && b == 'b')) return 'g';
	else if((a == 'g' && b == 'b') || (a == 'b' && b == 'g')) return 'r';
}

int solve(string s) {

	queue<P> q;
	map<string, int> m;
	q.push(P(s, 0));

	while (!q.empty()) {
		P p = q.front();
		q.pop();
		if(m[p.first]) continue;
		string now = p.first;
		if (judge(now)) return p.second;
		m[p.first] = p.second;
		for (int i = 0; i < now.size() - 1; ++i) {
			if (now[i] != now[i+1]){
				char temp;
				string next;
				temp = color(now[i], now[i + 1]);
				next = now;
				next[i] = next[i + 1] = temp;
				q.push(P(next, p.second + 1));
			}
		}
	}
	return -1;
}

int main() {
	string worm;
	while (cin >> worm) {
		if (worm == "0") break;
		int count = solve(worm);
		if (count == -1) cout << "NA" << endl;
		else cout << count << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<string>
#include<queue>
#include<unordered_map>
#include<map>
#define P pair<string,int>
#define p pair<char,char>
using namespace std;

int main()
{
	map<p, char>M;
	M[p('b', 'g')] = 'r';
	M[p('g', 'b')] = 'r';
	M[p('b', 'r')] = 'g';
	M[p('r', 'b')] = 'g';
	M[p('r', 'g')] = 'b';
	M[p('g', 'r')] = 'b';
	string a;
	while (cin >> a, a != "0") {
		unordered_map<string, int>U;
		queue<P>Q;
		Q.push(P(a, 1));
		while (Q.size()) {
			P c = Q.front(); Q.pop();
			bool d = true;
			for (int e = 1; e < c.first.length(); e++)if (c.first[e - 1] != c.first[e])d = false;
			if (d) { cout << c.second - 1 << endl; break; }
			for (int e = 1; e < c.first.length(); e++) {
				if (c.first[e - 1] != c.first[e]) {
					string copy = c.first;
					copy[e - 1] = copy[e] = M[p(c.first[e - 1], c.first[e])];
					if (U[copy] == 0) { U[copy] = c.second + 1; Q.push(P(copy,U[copy])); }
				}
			}
		}
	}
}