121. 买卖股票的最佳时机 - 力扣（LeetCode）

class Solution {public int maxProfit(int[] prices) {if(prices.length ==0){return 0;}int[][] dp = new int[prices.length][2];dp[0][0] = 0;dp[0][1] = -prices[0];for(int i=1;i<prices.length;i++){dp[i][0] = Math.max(dp[i-1][0],prices[i]+dp[i-1][1]);dp[i][1] = Math.max(-prices[i],dp[i-1][1]);}return dp[prices.length-1][0];}
}

122. 买卖股票的最佳时机 II - 力扣（LeetCode）

class Solution {public int maxProfit(int[] prices) {if(prices.length ==0){return 0;}int[][] dp = new int[prices.length][2];dp[0][0] = 0;dp[0][1] = -prices[0];for(int i=1;i<prices.length;i++){dp[i][0] = Math.max(dp[i-1][0],prices[i]+dp[i-1][1]);dp[i][1] = Math.max(dp[i-1][0]-prices[i],dp[i-1][1]);}return dp[prices.length-1][0];}
}

123. 买卖股票的最佳时机 III - 力扣（LeetCode） 

class Solution {public int maxProfit(int[] prices) {if(prices.length == 0){return 0;}int[][] dp = new int[prices.length][4];dp[0][0] = -prices[0];      //第i天持有第一次dp[0][1] = 0;               //第i天卖出第一次dp[0][2] = -prices[0];      //第i天持有第二次dp[0][3] = 0;               //第i天卖出第二次for(int i=1;i<prices.length;i++){dp[i][0] = Math.max(dp[i-1][0],-prices[i]);dp[i][1] = Math.max(dp[i-1][1],prices[i] + dp[i-1][0]);dp[i][2] = Math.max(dp[i-1][2],-prices[i]+dp[i-1][1]);dp[i][3] = Math.max(dp[i-1][3],prices[i]+dp[i-1][2]);}return Math.max(dp[prices.length-1][1],dp[prices.length-1][3]);}
}