188. 买卖股票的最佳时机 IV

public int maxProfit(int k, int[] prices) { // dp[i][k][0] = max(dp[i-1][k][0], dp[i-1][k][1] + prices[i]); // dp[i][k][1] = max(dp[i-1][k][1], dp[i-1][k-1][0] - prices[i]); int n = prices.length; if (n <= 1) return 0; if (k >= n / 2) { // 交易次数无限制 可以认为 k 等同于 无限大 // dp[i][0] = max(dp[i-1][0], dp[i-1][1] + prices[i]); // dp[i][1] = max(dp[i-1][1], dp[i-1][0] - prices[i]); int[] dp = new int[2]; dp[0] = 0; dp[1] = -prices[0]; for (int i = 1; i < n; i++) { dp[0] = Math.max(dp[0], dp[1] + prices[i]); dp[1] = Math.max(dp[1], dp[0] - prices[i]); } return dp[0]; } else { int[][] dp = new int[k+1][2]; for (int i = 1; i <= k; i++) { dp[i][1] = -prices[0]; } for (int i = 1; i < n; i++) { for (int j = 1; j <= k; j++) { dp[j][0] = Math.max(dp[j][0], dp[j][1] + prices[i]); dp[j][1] = Math.max(dp[j][1], dp[j-1][0] - prices[i]); } } return dp[k][0]; } }