代码随想录Day48：买卖股票的最佳时机、买卖股票的最佳时机II

class Solution {
public:
    /*
        dp[i][0]第i天持有股票所得的最大现金；
        dp[i][1]第i天不持有股票所得的最大现金；
        dp[i][0] = max(dp[i-1][0], - prices[i]);
        dp[i][1] = max(dp[i-1][1], dp[i-1][0] + prices[i]);
    */
    int maxProfit(vector<int>& prices) {
        int len = prices.size();
        vector<vector<int>> dp(len, vector<int>(2, 0));
        dp[0][0] = - prices[0];
        dp[0][1] = 0;
        for(int i = 1; i < len; i++){
            dp[i][0] = max(dp[i-1][0], - prices[i]);
            dp[i][1] = max(dp[i-1][1], dp[i-1][0] + prices[i]);
        }
        return dp[len-1][1];
    }
};

class Solution {
public:
    /*
        dp[i]为第i天的最大利润；
        dp[i] = max(dp[i - 1], dp[i - 1] + prices[i] - prices[i - 1]);
    */
    int maxProfit(vector<int>& prices) {
        int size = prices.size();
        vector<int> dp(size);
        dp[0] = 0;
        for(int i = 1; i < size; i++){
            dp[i] = max(dp[i - 1], dp[i - 1] + prices[i] - prices[i - 1]);
        }
        return dp[size - 1];
    }
};

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int size = prices.size();
        vector<vector<int>> dp(size, vector<int>(2));
        dp[0][0] = - prices[0];
        dp[0][1] = 0;
        for(int i = 1; i < size; i++){
            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]);
        }
        return dp[size - 1][1];
    }
};