Add the solution for the problem "#122 Best Time to Buy and Sell Stoc…

…k II".

src/leetcode.rs

@@ -286,6 +286,7 @@ mod q103_binary_tree_zipzag_level_order_traversal;
 mod q107_binary_tree_level_order_traversal_ii;
 mod q10_regular_expression_matching;
 mod q11_container_with_most_water;
+mod q122_best_time_to_buy_and_sell_stock_ii;
 mod q126_word_ladder_ii;
 mod q127_word_ladder;
 mod q12_integer_to_roman;
@@ -395,7 +396,6 @@ mod day_30_leetcoding_challenge;
 // mod q1046_last_stone_weight;
 // mod q155_min_stack;
 // mod q876_middle_of_the_linked_list;
-// mod q122_best_time_to_buy_and_sell_stock_ii;
 // mod q283_move_zeroes;
 // mod q136_single_number;
 // mod q202_happy_number;

src/leetcode/q122_best_time_to_buy_and_sell_stock_ii.rs

@@ -0,0 +1,43 @@
+/**
+ * 122. Best Time to Buy and Sell Stock II
+ *
+ * Say you have an array for which the ith 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.
+ */
+
+fn max_profit(prices: Vec<i32>) -> i32 {
+  let mut sum = 0;
+  for i in 1..prices.len() {
+    sum += 0.max(prices[i] - prices[i - 1]);
+  }
+  sum
+}
+
+#[test]
+fn q122_test() {
+  assert_eq!(max_profit(vec![7, 1, 5, 3, 6, 4]), 7);
+  assert_eq!(max_profit(vec![1, 2, 3, 4, 5]), 4);
+  assert_eq!(max_profit(vec![7, 6, 4, 3, 1]), 0);
+}