# 122 Best Time to Buy and Sell Stock II

input一樣是一個array，裡面是某股票每天的價錢，可以無限制買進賣出，問最高總利潤是多少

• idea: 一開始觀察了幾個case，發現只要一直更新min，一遇到比min大的就立刻賣，再把min設為Integer.MAX_VALUE，一般的case都可以對

  [7,1,4,3,6,5]
  
  min = 1
  price[i] = 4
  sum += 3
  
  min = 3
  price[i] = 5
  sum += 2
  
  最後 sum = 5
  ===================
  
  但如果有連續增加的數字會有錯誤
  [7,1,4,5,6,8]
  
  min = 1
  price[i] = 4
  sum += 3
  
  min = 5
  price[i] = 6
  sum += 1
  
  得到 sum = 4，但正確答案應該是 sum = 8-1 = 7
  

  觀察一下發現，(4-1) + (5-4) + (6-5) + (8-6) = 3+1+1+2 = 7，所以只要把重設min的方式改成min = price[i]就可以了。

• pseudocode:

  //keep min, sum
  //for all price in prices
  //  if price[i] < min, update min, 
  //  else min = price[i]; sum += price[i] - min;
  

• code:

  public class Solution {
    public int maxProfit(int[] prices) {
        int min = Integer.MAX_VALUE;
        int sum = 0;
  
        for(int i=0; i<prices.length; i++){
            if(prices[i] < min){
                min = prices[i];
            }else{
                sum += (prices[i] - min);
                min = prices[i];
            }
        }
        return sum;
    }
  }