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121. Best Time to Buy and Sell Stock
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 (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.
Note that you cannot sell a stock before you buy one.
Example 1:
Input: [7,1,5,3,6,4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 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 Explanation: In this case, no transaction is done, i.e. max profit = 0.
思路分析
一次遍历，在遍历中找最大值减去最小值即可。
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/**
* Runtime: 1 ms, faster than 69.16% of Java online submissions for Best Time to Buy and Sell Stock.
* Memory Usage: 42.6 MB, less than 5.31% of Java online submissions for Best Time to Buy and Sell Stock.
*
* Copy from: https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/solution/yi-ge-fang-fa-tuan-mie-6-dao-gu-piao-wen-ti-by-lab/[一个方法团灭 6 道股票问题 - 最佳买卖股票时机含冷冻期 - 力扣（LeetCode）]
*
* @author D瓜哥 · https://www.diguage.com
* @since 2020-01-01 13:01
*/
public int maxProfitDp(int[] prices) {
int dp0 = 0;
int dp1 = Integer.MIN_VALUE;
for (int i = 0; i < prices.length; i++) {
dp0 = Math.max(dp0, dp1 + prices[i]);
dp1 = Math.max(dp1, - prices[i]);
}
return dp0;
}
/**
* Runtime: 3 ms, faster than 19.73% of Java online submissions for Best Time to Buy and Sell Stock.
* Memory Usage: 42.7 MB, less than 5.31% of Java online submissions for Best Time to Buy and Sell Stock.
*
* Copy from: https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/solution/yi-ge-fang-fa-tuan-mie-6-dao-gu-piao-wen-ti-by-lab/[一个方法团灭 6 道股票问题 - 最佳买卖股票时机含冷冻期 - 力扣（LeetCode）]
*/
public int maxProfitDpTable(int[] prices) {
if (Objects.isNull(prices) || prices.length == 0) {
return 0;
}
int length = prices.length;
int[][] dp = new int[length][2];
dp[0][0] = 0;
dp[0][1] = -prices[0];
for (int i = 1; i < length; i++) {
dp[i][0] = Math.max(dp[i - 1][0], dp[i - 1][1] + prices[i]);
dp[i][1] = Math.max(dp[i - 1][1], -prices[i]);
}
return dp[length - 1][0];
}
/**
* Runtime: 0 ms, faster than 100.00% of Java online submissions for Best Time to Buy and Sell Stock.
*
* Memory Usage: 37.3 MB, less than 100.00% of Java online submissions for Best Time to Buy and Sell Stock.
*/
public int maxProfit(int[] prices) {
int minPrice = Integer.MAX_VALUE;
int maxProfit = 0;
for (int i = 0; i < prices.length; i++) {
if (prices[i] < minPrice) {
minPrice = prices[i];
} else if (prices[i] - minPrice > maxProfit) {
maxProfit = prices[i] - minPrice;
}
}
return maxProfit;
}
/**
* Runtime: 198 ms, faster than 8.08% of Java online submissions for Best Time to Buy and Sell Stock.
*
* Memory Usage: 38.5 MB, less than 76.99% of Java online submissions for Best Time to Buy and Sell Stock.
*/
public int maxProfitBruteForce(int[] prices) {
if (Objects.isNull(prices) || prices.length < 2) {
return 0;
}
int maxProfit = 0;
for (int i = 0; i < prices.length - 1; i++) {
for (int j = i + 1; j < prices.length; j++) {
int profit = prices[j] - prices[i];
if (profit > maxProfit) {
maxProfit = profit;
}
}
}
return maxProfit;
}
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/**
* @author D瓜哥 · https://www.diguage.com
* @since 2024-09-15 07:44:20
*/
public int maxProfit(int[] prices) {
int result = 0;
int min = 100000;
for (int p : prices) {
min = Math.min(min, p);
result = Math.max(result, p - min);
}
return result;
}