lintcode-medium-Best Time to Buy and Sell Stock III

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.

 

Given an example [4,4,6,1,1,4,2,5], return 6.

 

这题和I差不多，用两个数组l2r和r2l记录：第i天前最多做一次交易的最大获利，以及第i天之后最多做一次交易的最大获利。最后结果是两个数组对应的数的和的最大值

class Solution {
    /**
     * @param prices: Given an integer array
     * @return: Maximum profit
     */
    public int maxProfit(int[] prices) {
        // write your code here
        
        if(prices == null || prices.length < 2)
            return 0;
        
        int[] l2r = new int[prices.length];
        int[] r2l = new int[prices.length];
        
        l2r[0] = 0;
        r2l[prices.length - 1] = 0;
        int min = prices[0];
        int max = prices[prices.length - 1];
        
        for(int i = 1; i < prices.length; i++){
            if(prices[i] < min)
                min = prices[i];
            
            l2r[i] = Math.max(l2r[i - 1], prices[i] - min);
        }
        
        for(int i = prices.length - 2; i >= 0; i--){
            if(prices[i] > max)
                max = prices[i];
            
            r2l[i] = Math.max(r2l[i + 1], max - prices[i]);
        }
        
        int result = 0;
        
        for(int i = 0; i < prices.length; i++){
            if(l2r[i] + r2l[i] > result)
                result = l2r[i] + r2l[i];
        }
        
        return result;
    }
};