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Commit a231349

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121 best time to buy and sell stock solved. (#21)
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‎README.md

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* [75. Sort Colors](./src/0075_sort_colors/sort_colors.go)   *`sort;`*  *`array`*
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* [80. Remove Duplicates from Sorted Array II](./src/0080_remove_duplicates_from_sorted_array2/rdfsa2.go)   *`double index;`*  *`array`*
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* [88. Merge Sorted Array](./src/0088_merge_sorted_array/msa.go)   *`sort;`*  *`array`*
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* [121. Best Time to Buy and Sell Stock](src/0121_best_time_to_buy_and_sell_stock/maxprofit.go)   *`dynamic programming;`*  *`array`*
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* [167. Two Sum II - Input array is sorted](./src/0167_two_sum2/two_sum2.go)   *`double index;`*  *`binary search`*
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* [209. Minimum Size Subarray Sum](./src/0209_minimum_size_subarray_sum/minimum_size_subarray_sum.go)   *`sliding window`*
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* [215. Kth Largest Element in an Array](./src/0215_kth_largest_element_in_an_array/kthleiaa.go)   *`sort`*
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/*
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121. Best Time to Buy and Sell Stock
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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
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(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.
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*/
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// time: 2018年12月28日
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package maxprofit
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// dynamic programming
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// for every price, find the max profit, then record the current minimum price.
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// time complexity: O(n)
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// space complexity: O(1)
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func maxProfit(prices []int) int {
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n := len(prices)
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if 0 == n || 1 == n {
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return 0
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}
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var (
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res int
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minPrice = prices[0]
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)
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for _, price := range prices {
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if price - minPrice > res {
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res = price - minPrice
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}
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if price < minPrice {
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minPrice = price
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}
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}
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return res
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}
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// brute force
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// time complexity: O(n^2)
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// space complexity: O(1)
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func maxProfit1(prices []int) int {
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n := len(prices)
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if 0 == n || 1 == n {
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return 0
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}
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res := 0
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for i := 1; i < n; i++ {
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for j := 0; j < i; j++ {
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if prices[i]-prices[j] > res {
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res = prices[i] - prices[j]
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}
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}
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}
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return res
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}
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package maxprofit
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import "testing"
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func TestMaxProfit(t *testing.T) {
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testCases := [][]int{
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{7, 1, 5, 3, 6, 4},
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{5, 3, 2, 2, 5, 7, 9, 4},
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{},
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{3},
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{5, 3, 2, 2, 5, 7, 9, 4,5, 3, 2, 2, 5, 7, 9, 4},
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{2,4,1,11,7},
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}
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expected := []int{5, 7, 0, 0,7,10}
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for index, data := range testCases {
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if res := maxProfit(data); res != expected[index] {
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t.Errorf("expected %d, got %d", expected[index], res)
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}
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}
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}
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func TestMaxProfit1(t *testing.T) {
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testCases := [][]int{
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{7, 1, 5, 3, 6, 4},
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{5, 3, 2, 2, 5, 7, 9, 4},
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{},
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{3},
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}
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expected := []int{5, 7, 0, 0}
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for index, data := range testCases {
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if res := maxProfit1(data); res != expected[index] {
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t.Errorf("expected %d, got %d", expected[index], res)
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}
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}
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}

‎src/README.md

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|0111|[Minimum Depth of Binary Tree](./0111_minimum_depth_of_binary_tree/minimum_depth_of_binary_tree.go)|Easy|*`binary tree`*|
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|0112|[Path Sum](./0112_path_sum/path_sum.go)|Easy|*`binary tree`*|
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|0120|[Triangle](./0120_triangle/triangle.go)|Medium|*`dynamic programming;`* *` dfs`*|
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|0121|[121. Best Time to Buy and Sell Stock](0121_best_time_to_buy_and_sell_stock/maxprofit.go)|Easy||
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|0125|[Valid Palindrome](0125_valid_palindrome/valid_palindrome.go)|Easy||
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|0167|[Two Sum II - Input array is sorted](./0167_two_sum2/two_sum2.go)|Easy|*`对撞指针(双索引)`*|
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|0198|[House Robber](./0198_house_robber/house_robber.go)|Easy|*`memory search;`* *`dynamic programming`*|

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