[LeetCode] 009: Best Time to Buy and Sell Stock II

[Problem]

Say you have an array for which the i^th element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times). However, you may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

[Analysis]
找出每一个递增区间，累加所有递增区间的递增和。

[Solution]

class Solution {
public:
    int maxProfit(vector<int> &prices) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int minPrice = INT_MAX, profit = 0;
        for(int i = 0; i < prices.size(); ++i){
            // initial the minPrice
            if(i == 0){
                minPrice = prices[i];
            }
            else{
                // increasing
                if(prices[i] >= prices[i-1]){
                    minPrice = min(minPrice, prices[i]);
                }
                // descrease
                else{
                    profit += prices[i-1] - minPrice;
                    minPrice = prices[i];
                }
            }
        }
        
        // add the last increasing stock
        if(prices.size() > 0){
            profit += prices[prices.size()-1] - minPrice;
        }
        return profit;
    }
};

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