leetcode(121-123)买股票的最佳时机

1、

class Solution {
    public int maxProfit(int[] prices) {
        int len = prices.length;
        if(len<=1){
            return 0;
        }
        int min = prices[0];
        int max = 0;
        for(int i=1;i<len;++i){
            if(prices[i]-min>max){
               max =  prices[i]-min;
            }
            if(prices[i]<min){
               min = prices[i]; 
            } 
        }
        return max;
    }
}

 2、

class Solution {
    public int maxProfit(int[] prices) {
        int maxprofit = 0;
        for (int i = 1; i < prices.length; i++) {
            if (prices[i] > prices[i - 1])
                maxprofit += prices[i] - prices[i - 1];
        }
        return maxprofit;
    }
}

 3、

class Solution {
        public int maxProfit(int[] prices) {
        int len = prices.length;
        int min;
        int max;
        int maxProfile = 0;
        int maxProfile1;
        int maxProfile2;
        List<Integer> list1 = new ArrayList<>();
        List<Integer> list2 = new ArrayList<>();
        List<Integer> profile1 = new ArrayList<>();
        int i=0;
        while(i<len-1){
            while(i<len-1&&prices[i]>=prices[i+1]) ++i;
            min = prices[i];
            while(i<len-1&&prices[i]<=prices[i+1]) ++i;
            max = prices[i];
            list1.add(min);
            list2.add(max);
        }
        int size = list1.size();
        if(size==0) {
            
        }else if(size==1){
            return list2.get(0) - list1.get(0);
        }else{
            min = list1.get(0);
            maxProfile1 = list2.get(0)-min;
            for(i=0;i<size-1;++i){
                if(i>0){
                    min = Math.min(list1.get(i),min);
                    maxProfile1 = Math.max(list2.get(i)-min,maxProfile1);
                }
                profile1.add(maxProfile1);
            }
            max = list2.get(size-1);
            maxProfile2 = max-list1.get(size-1);
            for(i=size-1;i>0;--i){
                if(i<size-1){
                    max = Math.max(max,list2.get(i));
                    maxProfile2 = Math.max(max-list1.get(i),maxProfile2);
                }
                maxProfile = Math.max(maxProfile, profile1.get(i-1)+maxProfile2);
            }
            
        }
        return maxProfile;
    }
}