leetcode 121 —— 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.

思路：贪心算法，定义当前最高点和当前最低点，从左往右遍历，当刷新最高点时，则刷新最大落差maxD，当刷新最低点时，则最高点最低点同时变为当前点。

class Solution {
public:
int maxProfit(vector<int>& prices) {
if (prices.size() <= 1) return 0;
int minP = prices[0];
int maxP = prices[0];
int maxD = 0;
for (int i = 1; i < prices.size(); i++){
if (prices[i]>maxP){
maxP = prices[i];
maxD = max(maxD,maxP - minP);
}
if (prices[i] < minP){
maxP = prices[i];
minP = prices[i];
}
}
return maxD;
}
};