1. function maxProfit(prices: number[]): number {
    2.     const cache: number[][][] = Array(prices.length)
    3.         .fill(0)
    4.         .map(() => [
    5.             [NaN, NaN],
    6.             [NaN, NaN],
    7.         ]);
    9.     function backtrack(day: number, status: number, freeze: boolean): number {
    10.         // base case
    11.         if (day >= prices.length) {
    12.             return 0;
    13.         }
    14.         // 是否是冷冻期
    15.         if (freeze) {
    16.             return backtrack(day + 1, status, !freeze);
    17.         }
    18.         // 命中缓存
    19.         if (!Number.isNaN(cache[day][status][0])) {
    20.             return cache[day][status][0];
    21.         }
    22.         if (status === 0) {
    23.             //  非持有状态
    24.             cache[day][status][0] = Math.max(
    25.                 -prices[day] + backtrack(day + 1, (status + 1) % 2, false),
    26.                 backtrack(day + 1, status, false)
    27.             );
    28.         } else {
    29.             // 持有状态
    30.             cache[day][status][0] = Math.max(
    31.                 prices[day] + backtrack(day + 1, (status + 1) % 2, true),
    32.                 backtrack(day + 1, status, false)
    33.             );
    34.         }
    35.         return cache[day][status][0];
    36.         // make progress
    37.     }
    39.     return backtrack(0, 0, false);
    40. }