minimumDistances.js

// source: https://www.hackerrank.com/challenges/minimum-distances/problem
// video: https://youtu.be/gKp8Aq9mm9E

function minimumDistances(a) {
    // stores each unique value as a key with a value of last index
    const val_last_i = {}
    
    let min_distance = Infinity;
    // loop through array and populate val_last_i
    for(let i = 0; i < a.length; i++){ // O(n)
        const val = a[i]
        if (val in val_last_i){
            // val is a duplicate...
            // calculate distance from last i
            const distance = i - val_last_i[val]
            // assign min distances when appropriate
            if (distance < min_distance){
                min_distance = distance
            }
        }
        val_last_i[val] = i
    }

    // if each value is unique, there are no duplicates
    // this is indicated by min_distance still being Infinity
    if (min_distance == Infinity){
        return -1
    }
    return min_distance // Total Time Complexity: O(n)
}