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top-100-liked/13/13_1_test.go

@@ -0,0 +1,47 @@
+package top100liked
+
+import "testing"
+
+// https://leetcode.cn/problems/best-time-to-buy-and-sell-stock/
+
+// 贪心
+func maxProfit(prices []int) int {
+	minPrice := prices[0] // 历史最低买入价
+	maxProfit := 0
+
+	for i := 1; i < len(prices); i++ {
+		// 如果今天卖，能赚多少？
+		profit := prices[i] - minPrice
+		maxProfit = max(maxProfit, profit)
+
+		// 更新历史最低价
+		minPrice = min(minPrice, prices[i])
+	}
+	return maxProfit
+}
+
+// 动态规划
+// dp[n][0] 第 n 天手中不持有股票时的最大利润
+// dp[n][1] 第 n 天手中持有股票时的最大利润
+// func maxProfit(prices []int) int {
+// 	n := len(prices)
+// 	if n == 0 {
+// 		return 0
+// 	}
+
+// 	dp := make([][2]int, n)
+// 	dp[0][0] = 0
+// 	dp[0][1] = -prices[0]
+
+// 	for i := 1; i < n; i++ {
+// 		dp[i][0] = max(dp[i-1][0], dp[i-1][1]+prices[i])
+// 		dp[i][1] = max(dp[i-1][1], -prices[i])
+// 	}
+
+// 	return dp[n-1][0]
+// }
+
+func TestS13_1(t *testing.T) {
+	println(maxProfit([]int{7, 1, 5, 3, 6, 4}))
+	println(maxProfit([]int{7, 6, 4, 3, 1}))
+}

top-100-liked/13/13_test.go

@@ -0,0 +1,43 @@
+package top100liked
+
+import "testing"
+
+// 爆内存
+// func maxSubArray(nums []int) int {
+// 	l := len(nums)
+// 	msa := make([][]int, l)
+// 	for i := range msa {
+// 		msa[i] = make([]int, l)
+// 	}
+// 	res := nums[0]
+// 	for i, v := range nums {
+// 		msa[i][i] = v
+// 		res = max(res, v)
+// 	}
+// 	for i := range l {
+// 		for j := i + 1; j < l; j++ {
+// 			msa[i][j] = msa[i][j-1] + nums[j]
+// 			res = max(res, msa[i][j])
+// 		}
+// 	}
+// 	return res
+// }
+
+func maxSubArray(nums []int) int {
+	dp := make([]int, len(nums))
+	dp[0] = nums[0]
+	maxSoFar := nums[0]
+
+	for i := 1; i < len(nums); i++ {
+		dp[i] = max(nums[i], dp[i-1]+nums[i])
+		maxSoFar = max(maxSoFar, dp[i])
+	}
+	return maxSoFar
+}
+
+func TestS13(t *testing.T) {
+	println(maxSubArray([]int{-2, 1, -3, 4, -1, 2, 1, -5, 4}))
+	println(maxSubArray([]int{1}))
+	println(maxSubArray([]int{5, 4, -1, 7, 8}))
+	println(maxSubArray([]int{-2, 1}))
+}