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121. Best Time to Buy and Sell Stock #21
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59 changes: 59 additions & 0 deletions
src/0121_best_time_to_buy_and_sell_stock/maxprofit.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,59 @@ | ||
| /* | ||
| 121. Best Time to Buy and Sell Stock | ||
| https://leetcode.com/problems/best-time-to-buy-and-sell-stock/ | ||
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| Say you have an array for which the ith element is the price of a given stock on day i. | ||
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| 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. | ||
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| Note that you cannot sell a stock before you buy one. | ||
| */ | ||
| // time: 2018年12月28日 | ||
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| package maxprofit | ||
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| // dynamic programming | ||
| // for every price, find the max profit, then record the current minimum price. | ||
| // time complexity: O(n) | ||
| // space complexity: O(1) | ||
| func maxProfit(prices []int) int { | ||
| n := len(prices) | ||
| if 0 == n || 1 == n { | ||
| return 0 | ||
| } | ||
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| var ( | ||
| res int | ||
| minPrice = prices[0] | ||
| ) | ||
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| for _, price := range prices { | ||
| if price - minPrice > res { | ||
| res = price - minPrice | ||
| } | ||
| if price < minPrice { | ||
| minPrice = price | ||
| } | ||
| } | ||
| return res | ||
| } | ||
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| // brute force | ||
| // time complexity: O(n^2) | ||
| // space complexity: O(1) | ||
| func maxProfit1(prices []int) int { | ||
| n := len(prices) | ||
| if 0 == n || 1 == n { | ||
| return 0 | ||
| } | ||
| res := 0 | ||
| for i := 1; i < n; i++ { | ||
| for j := 0; j < i; j++ { | ||
| if prices[i]-prices[j] > res { | ||
| res = prices[i] - prices[j] | ||
| } | ||
| } | ||
| } | ||
| return res | ||
| } |
39 changes: 39 additions & 0 deletions
src/0121_best_time_to_buy_and_sell_stock/maxprofit_test.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,39 @@ | ||
| package maxprofit | ||
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| import "testing" | ||
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| func TestMaxProfit(t *testing.T) { | ||
| testCases := [][]int{ | ||
| {7, 1, 5, 3, 6, 4}, | ||
| {5, 3, 2, 2, 5, 7, 9, 4}, | ||
| {}, | ||
| {3}, | ||
| {5, 3, 2, 2, 5, 7, 9, 4,5, 3, 2, 2, 5, 7, 9, 4}, | ||
| {2,4,1,11,7}, | ||
| } | ||
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| expected := []int{5, 7, 0, 0,7,10} | ||
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| for index, data := range testCases { | ||
| if res := maxProfit(data); res != expected[index] { | ||
| t.Errorf("expected %d, got %d", expected[index], res) | ||
| } | ||
| } | ||
| } | ||
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| func TestMaxProfit1(t *testing.T) { | ||
| testCases := [][]int{ | ||
| {7, 1, 5, 3, 6, 4}, | ||
| {5, 3, 2, 2, 5, 7, 9, 4}, | ||
| {}, | ||
| {3}, | ||
| } | ||
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| expected := []int{5, 7, 0, 0} | ||
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| for index, data := range testCases { | ||
| if res := maxProfit1(data); res != expected[index] { | ||
| t.Errorf("expected %d, got %d", expected[index], res) | ||
| } | ||
| } | ||
| } |
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