O(m+n) for HackerRank - Climbing the Leaderboard (https://www.hackerrank.com/challenges/climbing-the-leaderboard/problem)

climbing-the-leaderboard.js

// For https://www.hackerrank.com/challenges/climbing-the-leaderboard/problem

function climbingLeaderboard(scores, alice) {

    let positionsCount = 1;
    const uscores = [scores[0]]; // Unique scores only, shorter array
    scores.reduce((prev, curr) => {
        if (prev != curr) {
            positionsCount++;
            uscores.push(curr)
        }    
        return curr;
    })
    
    let prevScoreIndex = uscores.length; // Latest index + outside
    let prevScoreValue = uscores[uscores.length - 1] - 1; // Smallest value - something
    let positionPivot = positionsCount + 1; // Latest postion + outside
  
    const result = []; 
    alice.forEach((value) => {

        if (value > prevScoreValue) {
            // Alice's position has been improved
            
            let currentScore = uscores[prevScoreIndex - 1]; 
            let positionsToSkip = 0
            for (let i = prevScoreIndex - 1; i >= 0; i--) {
                // Increase positionsToSkip on every score value changes
                if (uscores[i] != currentScore) {
                    positionsToSkip++;
                    currentScore = uscores[i] 
                }

                // Search for index to add new value
                if (uscores[i] > value) { 
                    // Our value should be inserted into uscore[i + 1]
                    prevScoreIndex = i + 1;
                    prevScoreValue = value;
                    uscores[prevScoreIndex] = value;
                    positionPivot = positionPivot - positionsToSkip;
                    break;
                }

                if (i == 0) {
                    // New value is the same or higer than first/biggest one
                    prevScoreIndex = 0;
                    prevScoreValue = value;
                    uscores[prevScoreIndex] = value;
                    positionPivot = 1;
                }

            }
        }
      
        result.push(positionPivot);
    })

    return result;
}