Best Time to Buy and Sell Stock


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.


For each element, calculate the max difference with the former elements.


时间复杂度 O(n),空间复杂度 O(1)


public class Solution {
    public int maxProfit(int[] prices) {
        int n = prices.length;
        if (n <= 1) return 0;
        int res = 0, minVal = prices[0];
        for (int i = 1; i < n; ++i) {
            res = Math.max(res, prices[i] - minVal);
            minVal = Math.min(minVal, prices[i]);
        return res;