Program to find the Length of the longest substring without repeating characters in Golang

// Golang program to find the length of the
// longest substring without repeating
// characters

package main

import "fmt"

func longest_substring(s string, n int) string {

    var i int
    
    // starting point of
    // current substring.
    st := 0    
    
    // length of current substring.  
    currlen := 0 
    
    // maximum length substring 
    // without repeating  characters
    maxlen := 0  

    // starting index of 
    // maximum length substring.
    start := 0

    // this array works as the hash table
    // -1 indicates that element is not
    // present before else any value 
    // indicates its previous index
    pos := make([]int, 125)

    for i = 0; i < 125; i++ {

        pos[i] = -1
    }

    // storing the index
    // of first character
    pos[s[0]] = 0

    for i = 1; i < n; i++ {

        // If this character is not present in array,
        // then this is first occurrence of this
        // character, store this in array.
        if pos[s[i]] == -1 {
            pos[s[i]] = i
        } else {
        
            // If this character is present in hash then
            // this character has previous occurrence,
            // check if that occurrence is before or after
            // starting point of current substring.
            if pos[s[i]] >= st {

                // find length of current substring and
                // update maxlen and start accordingly.
                currlen = i - st
                if maxlen < currlen {

                    maxlen = currlen
                    start = st
                }
                // Next substring will start after the last
                // occurrence of current character to avoid
                // its repetition.

                st = pos[s[i]] + 1

            }
            // Update last occurrence of
            // current character.
            pos[s[i]] = i
        }

    }
    // Compare length of last substring 
    // with maxlen and update maxlen 
    // and start accordingly.
    if maxlen < i-st {

        maxlen = i - st
        start = st
    }
    
    // the required string
    ans := ""

    // extracting the string from 
    // [start] to [start+maxlen]
    for i = start; i < start+maxlen; i++ {
        ans += string(s[i])
    }

    return ans

}

func main() {

    var s string = "GEEKSFORGEEKS"
    var n int = len(s)

    // calling the function to 
    // get the required answer.
    var newString = longest_substring(s, n)
    
    // finding the length of the string
    var length int = len(newString)

    fmt.Println("Longest substring is: ", newString)
    fmt.Println("Length of the string: ", length)

}