1. function maxProfit(k: number, prices: number[]): number {
    2.     const cache: number[][][] = new Array(prices.length)
    3.         .fill(0)
    4.         .map(() => [Array(k).fill(-1), Array(k).fill(-1)]);
    5.     function backtrack(day: number, status: number, times: number): number {
    6.         // base case
    7.         if (day >= prices.length || times >= k) {
    8.             return 0;
    9.         }
    11.         if (cache[day][status][times] !== -1) {
    12.             return cache[day][status][times];
    13.         }
    14.         if (status === 0) {
    15.             // make progress  到哪里去， 去哪儿
    16.             // status 未持有
    17.             cache[day][status][times] = Math.max(
    18.                 -prices[day] + backtrack(day + 1, (status + 1) % 2, times),
    19.                 backtrack(day + 1, status, times)
    20.             );
    21.         } else {
    22.             // 持有
    23.             cache[day][status][times] = Math.max(
    24.                 prices[day] + backtrack(day + 1, (status + 1) % 2, times + 1),
    25.                 backtrack(day + 1, status, times)
    26.             );
    27.         }
    29.         return cache[day][status][times];
    30.     }
    32.     return backtrack(0, 0, 0);
    33. }