123. Best Time to Buy and Sell Stock III

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mob604757027d04 2018-11-06 07:43:00

文章标签 i++ 其他 文章分类 代码人生

Say you have an array for which the ith element is the price of a given stock on day i.
Design an algorithm to find the maximum profit. You may complete at most two transactions.
Note: You may not engage in multiple transactions at the same time (i.e., you must sell the stock before you buy again).
Example 1:
Input: [3,3,5,0,0,3,1,4]
Output: 6
Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3), profit = 3-0 = 3.
             Then buy on day 7 (price = 1) and sell on day 8 (price = 4), profit = 4-1 = 3.
Example 2:
Input: [1,2,3,4,5]
Output: 4
Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.
             Note that you cannot buy on day 1, buy on day 2 and sell them later, as you are
             engaging multiple transactions at the same time. You must sell before buying again.
Example 3:
Input: [7,6,4,3,1]
Output: 0
Explanation: In this case, no transaction is done, i.e. max profit = 0.




Time o(n^ 2)


class Solution {
    public int maxProfit(int[] prices) {
        int res = 0;
        int left = 0;
        int right = 0;
        for(int i = 0; i < prices.length; i++){
            left = stock1(prices, 0, i);
            right = stock1(prices, i + 1, prices.length - 1);
            res = Math.max(left + right, res);
        }
        return res;
    }
    private int stock1(int[] prices, int start, int end){
        int res = 0;
        int min = Integer.MAX_VALUE;
        for(int i = start; i <= end; i++){
            min = Math.min(min, prices[i]);
            res = Math.max(res, prices[i] - min);
        }
        return res;
    }
}


Solution 
Time o(n)  ?