训练营第五十天 | 123.买卖股票的最佳时机III ● 188.买卖股票的最佳时机IV

class Solution {
    public int maxProfit(int[] prices) {
        //一维
        int len = prices.length;
        if(prices == null || len == 0) return 0;
        int[] dp = new int[5];
        dp[1] = - prices[0];
        dp[3] = - prices[0];
        for(int i = 1; i < len; i++) {
            dp[1] = Math.max(dp[1], -prices[i]);//第一次持有
            dp[2] = Math.max(dp[2], dp[1] + prices[i]);//第一次不持有
            dp[3] = Math.max(dp[3], dp[2] - prices[i]);//第二次持有
            dp[4] = Math.max(dp[4], dp[3] + prices[i]);//第二次不持有
        }
        return dp[4];
    }
}

class Solution {
    public int maxProfit(int[] prices) {
        //二维
        int len = prices.length;
        if(prices == null || len == 0) return 0;
        int[][] dp = new int[len][5];
        dp[0][1] = - prices[0];
        dp[0][3] = - prices[0];
        for(int i = 1; i < len; i++) {
            dp[i][1] = Math.max(dp[i-1][1], -prices[i]);//第一次持有
            dp[i][2] = Math.max(dp[i-1][2], dp[i-1][1] + prices[i]);//第一次不持有
            dp[i][3] = Math.max(dp[i-1][3], dp[i-1][2] - prices[i]);//第二次持有
            dp[i][4] = Math.max(dp[i-1][4], dp[i-1][3] + prices[i]);//第二次不持有
        }
        return dp[len - 1][4];
    }
}

?

class Solution {
    public int maxProfit(int k, int[] prices) {
        int len = prices.length;
        //dp[天数][交易次数][股票状态] 
        if(prices == null || len == 0) return 0;
        int[][][] dp = new int[len][k+1][2];
        for(int i = 0; i <= k; i ++) {
            dp[0][i][1] = -prices[0]; 
        } 
        for(int i = 1; i < len; i++) {
            for(int j = 1; j <= k; j ++) {
                dp[i][j][0] = Math.max(dp[i-1][j][0], dp[i-1][j][1] + prices[i]);
                dp[i][j][1] = Math.max(dp[i-1][j][1], dp[i-1][j-1][0] - prices[i]);
            }
        }
        return dp[len-1][k][0];
    }
}

?

class Solution {
    public int maxProfit(int k, int[] prices) {
        int len = prices.length;
        //dp[交易次数][股票状态] 
        if(prices == null || len == 0) return 0;
        int[][] dp = new int[k+1][2];
        for(int i = 0; i <= k; i ++) {
            dp[i][1] = -prices[0]; 
        } 
        for(int i = 1; i < len; 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];
    }
}

class Solution {
    public int maxProfit(int k, int[] prices) {
        int len = prices.length;
        //dp[天数][股票状态] 
        if(prices == null || len == 0) return 0;
        int[][] dp = new int[len][2*k+1];
        for(int i = 1; i < 2 * k; i += 2) {
            dp[0][i] = -prices[0]; 
        } 
        for(int i = 1; i < len; i++) {
            for(int j = 0; j < 2 * k; j += 2) {
                dp[i][j+1] = Math.max(dp[i-1][j+1], dp[i-1][j] - prices[i]);
                dp[i][j+2] = Math.max(dp[i-1][j+2], dp[i-1][j+1] + prices[i]);
            }
        }
        return dp[len-1][2*k];
    }
}