leetcode 122. Best Time to Buy and Sell Stock II

題目122. Best Time to Buy and Sell Stock II
標籤： 貪心

思路

找到除了第一個點的所有峯值，然後，對於每一個峯值，減去與前一個峯值（包括第一個點，如果它也是峯值的話）之間的山谷值得到差值，將所有的差值加起來就是最大收益

實現

# include <iostream>
# include <vector>

using namespace std;


class Solution {
public:
    int maxProfit(vector<int>& prices) {
       int size = prices.size();
       if(size <= 1) return 0;
       int ret = 0;
       int last_max = -1, last_min = prices[0];
       for(int i = 1; i < size; i++) {
            if(prices[i] <= last_min && last_max == -1) last_min = prices[i];
            else if(prices[i] > last_min && prices[i] >= last_max) last_max = prices[i];
            else { // get a valid and best last_min and last_max
                ret += last_max - last_min;
                last_min = prices[i];
                last_max = -1;          
            }
        }
        // the last case
        if(last_max != -1) ret += last_max - last_min;
        return ret;
    }
};