leetcode 62: Best Time to Buy and Sell Stock III

Best Time to Buy and Sell Stock IIINov 7 '12

Say you have an array for which the i^th 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 (ie, you must sell the stock before you buy again).

 

 

public class Solution {
    public int maxProfit(int[] prices) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int sz = prices.length;
        if(sz<=1) return 0;
        
        int[] dp1 = new int[sz];
        int[] dp2 = new int[sz];
        
        int min = prices[0];
        int max = prices[sz-1];
        dp1[0] = 0;
        dp2[sz-1] = 0;
        for(int i=1; i<sz; i++) {
            dp1[i] = Math.max( dp1[i-1], prices[i]-min);
            min = Math.min( prices[i], min);
        }
        
        for( int i=sz-2; i>=0; i--) {
            dp2[i] = Math.max( dp2[i+1], max - prices[i] );
            max = Math.max( prices[i], max);
        }
        
        int rel=0;
        for( int i=0; i<sz; i++) {
            rel = Math.max(rel, dp1[i]+dp2[i]);
        }
        return rel;
    }
};