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class Solution {   public:    int maxProfit(vector
   
    & prices) {           if(prices.size()==0)return 0;        int buy,sell;        int sum = 0;        for(int i = 0; i < prices.size()-1; i++){               while(i < prices.size()-1 && prices[i]>=prices[i+1]){   //找峰谷                i++;            }            buy = prices[i];            while(i < prices.size()-1&&prices[i]<=prices[i+1]){   //找封底                i++;            }            sell = prices[i];            sum += sell - buy;//相减得到一次最大利益        }        return sum;    }};
   

时间复杂度O(n)

class Solution {   public:    int maxProfit(vector
   
    & prices) {           int sum = 0;                for(int i = 0; i < (int)prices.size()-1; i++){               if(prices[i+1]>prices[i]){   //通过方法二,规律为所有上升值的和                sum += prices[i+1] - prices[i];            }        }        return sum;    }};
   

时间复杂度O(n)