You are given two integer arrays prices and strategy, where: prices[i] is the price of a given stock on the ith day. strategy[i] represents a trading action on the ith day, where: -1 indicates buying one unit of the stock. 0 indicates holding the st

maxProfit.js

/**
 * Calculates the maximum profit achievable by applying a strategy
 * and replacing a window of size `k` with a new profit calculation.
 *
 * @param {number[]} prices - Array of prices over time.
 * @param {number[]} strategy - Strategy multipliers applied to each price.
 * @param {number} k - Size of the window to adjust.
 * @returns {number} Maximum profit achievable.
 */
var maxProfit = function(prices, strategy, k) {
    const n = prices.length;
    let maxProfit = 0;

    // Prefix sums for cumulative values and profits
    const prefixSumPrices = new Array(n);
    const prefixSumProfit = new Array(n);

    // Initialize prefix sums with the first element
    prefixSumPrices[0] = prices[0];
    prefixSumProfit[0] = prices[0] * strategy[0];

    // Build prefix sums for prices and profits
    for (let i = 1; i < n; i++) {
        prefixSumPrices[i] = prices[i] + prefixSumPrices[i - 1];
        prefixSumProfit[i] = prefixSumProfit[i - 1] + prices[i] * strategy[i];
    }

    // Current profit using the full strategy
    const baseProfit = prefixSumProfit[n - 1];
    maxProfit = baseProfit;

    // Try replacing each window of size k
    for (let left = 0; left <= n - k; left++) {
        const right = left + k - 1;

        // Profit contributed by the current window [left, right]
        let windowProfit = prefixSumProfit[right];
        if (left > 0) {
            windowProfit -= prefixSumProfit[left - 1];
        }

        // New profit if we replace the second half of the window
        const mid = left + Math.floor(k / 2) - 1;
        const newWindowProfit = prefixSumPrices[right] - prefixSumPrices[mid];

        // Adjusted profit: remove old window profit, add new window profit
        const adjustedProfit = baseProfit - windowProfit + newWindowProfit;

        // Track maximum profit
        maxProfit = Math.max(maxProfit, adjustedProfit);
    }

    return maxProfit;
};