122.best-time-to-buy-and-sell-stock-ii.go

/*
 * @lc app=leetcode id=122 lang=golang
 *
 * [122] Best Time to Buy and Sell Stock II
 *
 * https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/
 *
 * algorithms
 * Easy (58.22%)
 * Likes:    3487
 * Dislikes: 1901
 * Total Accepted:    744.1K
 * Total Submissions: 1.3M
 * Testcase Example:  '[7,1,5,3,6,4]'
 *
 * Say you have an array prices for which the i^th element is the price of a
 * given stock on day i.
 * 
 * Design an algorithm to find the maximum profit. You may complete as many
 * transactions as you like (i.e., buy one and sell one share of the stock
 * multiple times).
 * 
 * Note: You may not engage in multiple transactions at the same time (i.e.,
 * you must sell the stock before you buy again).
 * 
 * Example 1:
 * 
 * 
 * Input: [7,1,5,3,6,4]
 * Output: 7
 * Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5), profit
 * = 5-1 = 4.
 * Then buy on day 4 (price = 3) and sell on day 5 (price = 6), profit = 6-3 =
 * 3.
 * 
 * 
 * Example 2:
 * 
 * 
 * Input: [1,2,3,4,5]
 * Output: 4
 * Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit
 * = 5-1 = 4.
 * Note that you cannot buy on day 1, buy on day 2 and sell them later, as you
 * are
 * engaging multiple transactions at the same time. You must sell before buying
 * again.
 * 
 * 
 * Example 3:
 * 
 * 
 * Input: [7,6,4,3,1]
 * Output: 0
 * Explanation: In this case, no transaction is done, i.e. max profit = 0.
 * 
 * 
 * Constraints:
 * 
 * 
 * 1 <= prices.length <= 3 * 10 ^ 4
 * 0 <= prices[i] <= 10 ^ 4
 * 
 * 
 */
package leetgo

// @lc code=start
func maxProfit(prices []int) int {
    if len(prices) == 0 {
		return 0
	}
	pre := prices[0]
	res := 0
	for _, item := range prices {
		if item - pre > 0 {
			res += item - pre
		}
		pre = item
	}
	return res
}

// @lc code=end