largest_product_in_series.go

package main

/* The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

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Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
*/

import (
	"fmt"
	"strconv"
	"strings"
)

var numbers = []int{}
var max uint64 = 0

func maxmultiple(startindex int, endindex int) {
	var mul uint64 = 1
	for i := startindex; i < endindex; i++ { // multiple the 13 digits
		mul *= uint64(numbers[i])
	}
	if mul > max { // if max then update
		max = mul
	}
}

func main() {
	str := ""
	fmt.Scan(&str)
	s := strings.Split(str, "")

	for _, v := range s { // convert the slice of string to slice of int
		if no, err := strconv.Atoi(v); err == nil {
			numbers = append(numbers, no)
		}
	}

	startindex := 0
	endindex := 0
	for i, v := range numbers {
		if v == 0 { // check if the number is zero
			startindex = i + 1 // if yes update the start and end index to index+1
			endindex = i + 1
		} else {
			endindex += 1                  // else update the end index to index+1
			if endindex-startindex == 13 { // check we have got 13 consecutive digit
				maxmultiple(startindex, endindex)
				startindex += 1 // update the start index by adding one in it, to maintain 13 lenght
			}
		}
	}
	fmt.Println(max)

}