BestTimetoBuyandSellStock.java

package leetcode;

/**
 * @author eko
 * @date 2018/10/30 8:26 PM
 *
 * 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 (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.
 *
 * Note that you cannot sell a stock before you buy one.
 *
 * Example 1:
 *
 * Input: [7,1,5,3,6,4]
 * Output: 5
 * Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 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
 * Explanation: In this case, no transaction is done, i.e. max profit = 0.
 */
public class BestTimetoBuyandSellStock {
    public static void main(String[] args) {
        int[] prices = {7, 1, 5, 3, 6, 4};
        int res = new BestTimetoBuyandSellStock().maxProfit(prices);
        System.out.println(res);
    }

    public int maxProfit(int[] prices) {
        int max = 0;
        int lowInex = 0;
        for (int i = 1; i < prices.length; i++) {
            if (prices[lowInex] > prices[i]) lowInex = i;
            else max = Math.max(prices[i] - prices[lowInex], max);
        }
        return max;
    }
}