[leetcode]Best Time to Buy and Sell Stock

一趟遍历。O(n)。期间记录最小的价格min的值并不断比较更新最大差价。

public class Solution {

    public int maxProfit(int[] prices) {

        // Start typing your Java solution below

        // DO NOT write main() function

        if (prices.length < 2) return 0;

        

        int min = prices[0];

        int max = 0;

        for (int i = 1; i < prices.length; i++) {

            if (prices[i] < min) {

        		min = prices[i];

        	}

        	else

        	{

        		int val = prices[i] - min;

        		if (val > max) max = val;

        	}

        }

        return max;

    }

}

第二刷：

class Solution {

public:

    int maxProfit(vector<int> &prices) {

        int m = 0;

        if (prices.size() == 0)

            return m;

        int minPrice = prices[0];

        for (int i = 0; i < prices.size(); i++) {

            if (prices[i] < minPrice)

                minPrice = prices[i];

            int x = prices[i] - minPrice;

            if (x > m)

                m = x;

        }

        return m;

    }

};