LeetCode 121. Best Time to Buy and Sell Stock

原题链接在这里：https://leetcode.com/problems/best-time-to-buy-and-sell-stock/

题目：

Say you have an array for which the ith 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.

题解：

Let local denotes up to i, maximum profit when last transaction must happend at i. If it is smaller than 0, reset as 0.

local = Math.max(local + diff, 0). 

Maintain the global maximum.

global = Math.max(local, global).

Time Complexity: O(n). Space: O(1).

AC Java:

public class Solution {
    public int maxProfit(int[] prices) {
        //采用局部最优和全局最优
        if(prices == null || prices.length <= 1){
            return 0;
        }
        int local = 0;
        int global = 0;
        for(int i = 1; i<prices.length; i++){
            local = Math.max(local+prices[i]-prices[i-1],0);
            global = Math.max(local,global);
        }
        return global;
    }
}

类似Maximum Subarray, Maximum Difference Between Increasing Elements.

跟上Best Time to Buy and Sell Stock II, Best Time to Buy and Sell Stock III, Best Time to Buy and Sell Stock IV, Best Time to Buy and Sell Stock with Cooldown, Best Time to Buy and Sell Stock with Transaction Fee.