Merge pull request neetcode-gh#338 from shehanck/main

leetcode-309 solution in Java

Author: SharmaTushar1

java/309-Best-Time-To-Buy-and-Sell-Stock-With-Cooldown.java

@@ -0,0 +1,29 @@
+class Solution {
+   public int maxProfit(int[] prices) {
+        Map<String, Integer> cache = new HashMap<>();
+        return dfs(prices, cache, 0, true);
+    }
+
+    public int dfs(int[] prices, Map<String, Integer> cache, int index, boolean buying) {
+        if (index >= prices.length) {
+            return 0;
+        }
+        String key = index+"-"+buying;
+
+        if (cache.containsKey(key)) {
+            return cache.get(key);
+        }
+
+        int cooldown = dfs(prices, cache, index + 1, buying);
+        int buyOsell = Integer.MIN_VALUE;
+
+        if (buying) {
+            buyOsell = dfs(prices, cache, index + 1, !buying) - prices[index];
+        } else {
+            buyOsell = dfs(prices, cache, index + 2, !buying) + prices[index];
+        }
+        
+        cache.put(key, Math.max(buyOsell, cooldown));        
+        return cache.get(key);
+    }
+}