Leetcode/各大家 -- 121. Best Time to Buy and Sell Stock

121. Best Time to Buy and Sell Stock

• Difficulty: Easy

https://leetcode.com/problems/best-time-to-buy-and-sell-stock/

Say you have an array for which the i^th element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Example 1:

Input: [7, 1, 5, 3, 6, 4]
Output: 5

max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)

Example 2:

Input: [7, 6, 4, 3, 1]
Output: 0

In this case, no transaction is done, i.e. max profit = 0.

Company: Amazon Microsoft Bloomberg Uber Facebook

解法：用Kanede's algorithm, compute max_ending_here if earn money add previous index + pirce[i]-prices[i-1]>0else0, track the overall max_so_far
相关题：http://rainykat.blogspot.com/2016/12/leetcodelinkedin-maximum-subarraydp-or.html
思路：DP， Kanede's algorithm(for max subarray)

public class Solution {
    public int maxProfit(int[] prices) {
        int n = prices.length;
        int max_so_far = 0,max_ending_here =0;//max sum of arr[0..i]
        for(int i = 1; i < n; i++){
           max_ending_here = Math.max(0,max_ending_here + prices[i]-prices[i-1]);
            max_so_far = Math.max(max_so_far,max_ending_here);
        }
        return max_so_far;
    }
}