121. Best Time to Buy and Sell Stock[Leetcode从零开刷]

题目来源：

leetcode

题目

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.

Example 1:

Input: [7, 1, 5, 3, 6, 4]
Output: 5

max. difference = 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

In this case, no transaction is done, i.e. max profit = 0.

题目解答：

简单的说，就是给一个数组，求最大的差值，只能用数组后面的减前面的。

所以，第一个被减数假设就是第一个数，遇到比它小的则换成这个小的。

用后面的大的减去被减数，记录最大的差值即可。

class Solution {
public int maxProfit(int[] prices) {
int n = prices.length;
int res = 0;
if(n==0) return res;
int bought = prices[0];
for(int i= 1;i<n;i++){
if(prices[i]>bought){
if(res < prices[i] - bought){
res = prices[i] - bought;
}
}
else
{
bought = prices[i];
}

}
return res;

}
}