Problem:
Score : 100 points

Problem Statement

In AtCoder City, there are three stations numbered 1, 2, and 3.

Each of these stations is operated by one of the two railway companies, A and B. A string S of length 3 represents which company operates each station. If S_i is A, Company A operates Station i; if S_i is B, Company B operates Station i.

To improve the transportation condition, for each pair of a station operated by Company A and one operated by Company B, there will be a bus service connecting them.

Determine if there is a pair of stations that will be connected by a bus service.

Constraints

Each character of S is A or B.

|S| = 3

Input

Input is given from Standard Input in the following format:

S

Output

If there is a pair of stations that will be connected by a bus service, print Yes; otherwise, print No.

Sample Input 1

ABA

Sample Output 1

Yes

Company A operates Station 1 and 3, while Company B operates Station 2.

There will be a bus service between Station 1 and 2, and between Station 2 and 3, so print Yes.

Sample Input 2

BBA

Sample Output 2

Yes

Company B operates Station 1 and 2, while Company A operates Station 3.

There will be a bus service between Station 1 and 3, and between Station 2 and 3, so print Yes.

Sample Input 3

BBB

Sample Output 3

No

Company B operates all the stations. Thus, there will be no bus service, so print No.

Solution in Go (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
	"io"
	"os"
)

func main() {
	fmt.Println(resolve(parseProblem(os.Stdin)))
}

func parseProblem(r io.Reader) (s string) {
	fmt.Fscanf(r, "%s", &s)
	return s
}

func resolve(s string) string {
	st := newByteSet(s)
	if st.size() > 1 {
		return "Yes"
	}
	return "No"
}

func newByteSet(input string) byteSet {
	s := newSet()
	for i := 0; i < len(input); i++ {
		s.add(input[i])
	}
	return s
}

type byteSet map[byte]none

func newSet() byteSet {
	return make(map[byte]none)
}

func (s byteSet) add(item byte) {
	s[item] = mark
}

func (s byteSet) doesContain(item byte) bool {
	_, ok := s[item]
	return ok
}

func (s byteSet) size() int {
	return len(s)
}

var mark none

type none struct{}