You are given the customer visit log of a shop represented by a 0-indexed string customers consisting only of characters 'N' and 'Y': if the ith character is 'Y', it means that customers come at the ith hour whereas 'N' indicates that no customers c

bestClosingTime.js

/**
 * Given a string of 'Y' (customer arrives) and 'N' (no customer),
 * find the hour to close the shop that minimizes penalty.
 *
 * Penalty rules:
 * - Staying open while no customers come → +1 penalty for each 'N'
 * - Closing early while customers would have come → +1 penalty for each 'Y'
 *
 * @param {string} customers
 * @return {number}
 */
var bestClosingTime = function (customers) {
    const n = customers.length;

    // Initial penalty: assume we close at hour 0 (never open).
    // That means every 'Y' is a missed customer → penalty += 1.
    let penalty = 0;
    for (let i = 0; i < n; i++) {
        if (customers[i] === 'Y') penalty++;
    }

    // Track best answer: [bestHour, bestPenalty]
    let best = [0, penalty];

    // Sweep through each possible closing hour 1..n
    for (let hour = 1; hour <= n; hour++) {
        // We "move" the boundary one step to the right.
        // customers[hour - 1] is now considered "open" instead of "closed".
        if (customers[hour - 1] === 'Y') {
            // Previously counted as a missed customer → remove penalty.
            penalty--;
        } else {
            // Now we stay open during an 'N' → add penalty.
            penalty++;
        }

        // Update best closing hour if penalty improves.
        if (penalty < best[1]) {
            best = [hour, penalty];
        }
    }

    return best[0];
};