309-Best-Time-To-Buy-And-Sell-Stock-With-Cooldown.js

/**
 * @param {number[]} prices
 * @return {number}
 */
var maxProfit = function (prices) {
    let dp = {}; // key=[i, buying] val=max_profit

    const dfs = (i, buying) => {
        if (i >= prices.length) return 0;
        if (dp[[i, buying]]) return dp[[i, buying]];

        const cooldown = dfs(i + 1, buying);
        if (buying) {
            const buy = dfs(i + 1, !buying) - prices[i];
            dp[[i, buying]] = Math.max(buy, cooldown);
        } else {
            sell = dfs(i + 2, !buying) + prices[i];
            dp[[i, buying]] = Math.max(sell, cooldown);
        }
        return dp[[i, buying]];
    };

    return dfs(0, true);
};