【启发】leetcode - 121. Best Time to Buy and Sell Stock 【动态规划 + 连续区间问题 + 试探性购买】

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.

分析及解答

public int maxProfit(int[] prices) {
if (prices == null || prices.length == 0) {
return 0;
}
int profit = 0, max = 0;
for (int i = 1; i < prices.length; i++) {
profit += prices[i] - prices[i - 1];
//【模拟】试探性买入。（假设可以多次购买，如果到某个地方赔了，那么重新开始）
//当在前面买了股票后，对于当前有削弱作用，我们就不会在前面买了。（重新开始买入）
if (profit < 0) {
profit = 0;
} else if (max < profit) {
max = profit;
}
}
return max;
}