309. Best Time to Buy and Sell Stock with Cooldown

Given daily stock prices, return the maximum profit from as many buy/sell transactions as you like, holding at most one share, where after selling you must wait one day (cooldown) before buying again.

Track the best profit ending each day in three states: hold (own a share), sold (just sold, cooling down tomorrow) and rest (free to buy). Each day's states come from yesterday's.

1function maxProfit(prices: number[]): number {
2  let hold = -Infinity, sold = 0, rest = 0;
3  for (const p of prices) {
4    const prevSold = sold;
5    sold = hold + p;                 // sell today
6    hold = Math.max(hold, rest - p); // keep holding, or buy from rest
7    // rest: cooldown ends (or keep resting)
8    rest = Math.max(rest, prevSold);
9  }
10  return Math.max(sold, rest);
11}

hold = −∞sold = 0rest = 0

prices

state per day


hold
sold
rest

Before day 0: can't hold, nothing sold.

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