/* Given a string of characters. Find the number of pairs of indices i and j (i <= j) between which there are no repeating characters. For the string "aba" the answer is 5: can be ASCII [0, 0] ("a") [0, 1] ("ab") [1, 1] ("b") [1, 2] ("ba") [2, 2] ("a") */

To solve the problem, you need to iterate over all substrings of the string and check that each substring contains no repeating characters. To do this efficiently, you can use a sliding window with two pointers and a set to track unique characters.

Example in Go:

func countUniqueSubstrings(s string) int {
    n := len(s)
    count := 0
    chars := make(map[byte]bool)
    j := 0

    for i := 0; i < n; i++ {
        for j < n && !chars[s[j]] {
            chars[s[j]] = true
            j++
        }
        count += j - i
        delete(chars, s[i])
    }
    return count
}

// Usage example:
// s := "aba"
// fmt.Println(countUniqueSubstrings(s)) // Outputs 5

Idea: expand the right pointer j while characters are unique, then move the left pointer i, removing characters from the set. The number of unique substrings starting at i is j - i.