Problem:
Score : 200 points

Problem Statement

You are given a string S consisting of uppercase English letters. Find the length of the longest ACGT string that is a substring (see Notes) of S.

Here, a ACGT string is a string that contains no characters other than A, C, G and T.

Notes

A substring of a string T is a string obtained by removing zero or more characters from the beginning and the end of T.

For example, the substrings of ATCODER include TCO, AT, CODER, ATCODER and (the empty string), but not AC.

Constraints

S is a string of length between 1 and 10 (inclusive).

Each character in S is an uppercase English letter.

Input

Input is given from Standard Input in the following format:

S

Output

Print the length of the longest ACGT string that is a substring of S.

Sample Input 1

ATCODER

Sample Output 1

3

Among the ACGT strings that are substrings of ATCODER, the longest one is ATC.

Sample Input 2

HATAGAYA

Sample Output 2

5

Among the ACGT strings that are substrings of HATAGAYA, the longest one is ATAGA.

Sample Input 3

SHINJUKU

Sample Output 3

0

Among the ACGT strings that are substrings of SHINJUKU, the longest one is (the empty string).

Solution in Go (1.14.1) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"sort"
	"strconv"
	"strings"
)

func main() {
	s := readString()

	tmp := 0
	ans := 0
	for i := 0; i < len(s); i++ {
		if string(s[i]) == "A" || string(s[i]) == "C" || string(s[i]) == "G" || string(s[i]) == "T" {
			tmp++
		} else {
			tmp = 0
		}
		ans = max(tmp, ans)
	}

	fmt.Println(ans)
}

/*-------------------utilities-------------------*/

func abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}

func min(x, y int) int {
	if x < y {
		return x
	}
	return y
}

func max(x, y int) int {
	if x > y {
		return x
	}
	return y
}

// func chmin(x *int, y int) bool {
// 	if *x > y {
// 		*x = y
// 		return true
// 	}
// 	return false
// }

// func chmax(x *int, y int) bool {
// 	if *x < y {
// 		*x = y
// 		return true
// 	}
// 	return false
// }

func gcd(a, b int) int {
	if b == 0 {
		return a
	}
	return gcd(b, a%b)
}

func lcm(a, b int) int {
	return (a * b) / gcd(a, b)
}

func permutations(arr []int) [][]int {
	var helper func([]int, int)
	res := [][]int{}

	helper = func(arr []int, n int) {
		if n == 1 {
			tmp := make([]int, len(arr))
			copy(tmp, arr)
			res = append(res, tmp)
		} else {
			for i := 0; i < n; i++ {
				helper(arr, n-1)
				if n%2 == 1 {
					tmp := arr[i]
					arr[i] = arr[n-1]
					arr[n-1] = tmp
				} else {
					tmp := arr[0]
					arr[0] = arr[n-1]
					arr[n-1] = tmp
				}
			}
		}
	}
	helper(arr, len(arr))
	return res
}

func isPrime(n int) bool {
	if n == 1 {
		return false
	}
	for i := 2; i*i <= n; i++ {
		if n%i == 0 {
			return false
		}
	}
	return true
}

func primeFactors(n int) []int {
	factors := make([]int, 0)
	i := 2
	for i*i <= n {
		r := n % i
		if r != 0 {
			i++
		} else if r == 0 {
			n /= i
			factors = append(factors, i)
		}
	}
	if n > 1 {
		factors = append(factors, n)
	}
	return factors
}

func divisor(n int) (res []int) {
	for i := 1; i*i <= n; i++ {
		if n%i == 0 {
			res = append(res, i)
			if i*i != n {
				res = append(res, n/i)
			}
		}
	}
	sort.Ints(res)
	return
}

func searchInts(a []int, k int) int {
	return binarySearch(len(a), func(i int) bool {
		return a[i] >= k
	})
}

func binarySearch(n int, f func(int) bool) int {
	i, j := 0, n
	for i < j {
		h := int(uint(i+j) >> 1)
		if !f(h) {
			i = h + 1
		} else {
			j = h
		}
	}
	return i
}

func reverseStr(s string) string {
	var b strings.Builder
	b.Grow(len(s))
	for i := len(s) - 1; i >= 0; i-- {
		b.WriteByte(s[i])
	}
	return b.String()
}

type Queue struct {
	items []int
}

func (q *Queue) push(item int) {
	q.items = append(q.items, item)
}

func (q *Queue) pop() {
	q.items = q.items[1:]
}

func (q *Queue) front() int {
	return q.items[0]
}

func (q *Queue) size() int {
	return len(q.items)
}

/*-------------------init-------------------*/

const (
	INF = 1000000000000000000
	MOD = 1e9 + 7
)

var (
	readString func() string
)

func init() {
	readString = newReadString(os.Stdin)
}

/*-------------------inputs-------------------*/

func readi() int {
	return int(readi64())
}

func readi64() int64 {
	i, err := strconv.ParseInt(readString(), 0, 64)
	if err != nil {
		panic(err.Error())
	}
	return i
}

func readf() float64 {
	f, err := strconv.ParseFloat(readString(), 64)
	if err != nil {
		panic(err.Error())
	}
	return f
}

func newReadString(ior io.Reader) func() string {
	r := bufio.NewScanner(ior)
	r.Buffer(make([]byte, 1024), int(1e+11))
	r.Split(bufio.ScanWords)

	return func() string {
		if !r.Scan() {
			panic("Scan failed")
		}
		return r.Text()
	}
}