121. The best time to buy and sell stocks

121. The best time to buy and sell stocks

Given an array prices , It's the first i Elements prices[i] Represents the number of shares in a given stock i Sky price .

You can only choose One day Buy this stock , And choose A different day in the future Sell the stock . Design an algorithm to calculate the maximum profit you can get .

Return the maximum profit you can make from the deal . If you can't make any profit , return 0 .

Example 1：

Input ：[7,1,5,3,6,4]

Output ：5

explain ： In the 2 God （ Stock price = 1） Buy when , In the 5 God （ Stock price = 6） Sell when , Maximum profit = 6-1 = 5 .

Note that profit cannot be 7-1 = 6, Because the selling price needs to be higher than the buying price ; meanwhile , You can't sell stocks before you buy them .

Example 2：

Input ：prices = [7,6,4,3,1]
Output ：0
explain ： under these circumstances , No deal is done , So the biggest profit is 0.

Tips ：

1 <= prices.length <= 105
0 <= prices[i] <= 104

reflection

First, let's assume that we sell stocks on the first day , That is, the current selling price of the stock is sellPrice

If the next i The stock price of days is lower than the stock price sold sellPrice = prices[i]

otherwise max = Math.max(max,prices[i]-sellPrice);

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