refactor 121

fishercoder1534 · fishercoder1534 · commit 96a1ff0b95c6 · 2021-09-15T09:51:13.000-07:00
diff --git a/src/main/java/com/fishercoder/solutions/_121.java b/src/main/java/com/fishercoder/solutions/_121.java
@@ -3,6 +3,31 @@
 public class _121 {
 
     public static class Solution1 {
+        /**
+         * My very original but not super optimal solution.
+         */
+        public int maxProfit(int[] prices) {
+            int[] maxPriceAfterThisDay = new int[prices.length];
+            int maxSell;
+            for (int i = prices.length - 1; i > 0; i--) {
+                maxSell = Math.max(maxPriceAfterThisDay[i], prices[i]);
+                maxPriceAfterThisDay[i] = maxSell;
+            }
+            int[] minPriceBeforeThisDay = new int[prices.length];
+            int minBuy = prices[0];
+            for (int i = 0; i < prices.length - 1; i++) {
+                minBuy = Math.min(prices[i], minBuy);
+                minPriceBeforeThisDay[i] = minBuy;
+            }
+            int maxPro = 0;
+            for (int i = 0; i < prices.length - 1; i++) {
+                maxPro = Math.max(maxPro, maxPriceAfterThisDay[i + 1] - minPriceBeforeThisDay[i]);
+            }
+            return maxPro;
+        }
+    }
+
+    public static class Solution2 {
         /**
          * The key here is that you'll have to buy first, before you can sell. That means, if the lower
          * price comes after a higher price, their combination won't work! Since you cannot sell first
diff --git a/src/test/java/com/fishercoder/_121Test.java b/src/test/java/com/fishercoder/_121Test.java
@@ -7,35 +7,41 @@
 import static junit.framework.Assert.assertEquals;
 
 public class _121Test {
-  private static _121.Solution1 solution1;
-  private static int[] prices;
-
-  @BeforeClass
-  public static void setup() {
-    solution1 = new _121.Solution1();
-  }
-
-  @Test
-  public void test1() {
-    prices = new int[] {7, 1, 5, 3, 6, 4};
-    assertEquals(5, solution1.maxProfit(prices));
-  }
-
-  @Test
-  public void test2() {
-    prices = new int[] {7, 6, 4, 3, 1};
-    assertEquals(0, solution1.maxProfit(prices));
-  }
-
-  @Test
-  public void test3() {
-    prices = new int[] {2, 4, 1};
-    assertEquals(2, solution1.maxProfit(prices));
-  }
-
-  @Test
-  public void test4() {
-    prices = new int[] {1, 2};
-    assertEquals(1, solution1.maxProfit(prices));
-  }
+    private static _121.Solution1 solution1;
+    private static _121.Solution2 solution2;
+    private static int[] prices;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _121.Solution1();
+        solution2 = new _121.Solution2();
+    }
+
+    @Test
+    public void test1() {
+        prices = new int[]{7, 1, 5, 3, 6, 4};
+        assertEquals(5, solution1.maxProfit(prices));
+        assertEquals(5, solution2.maxProfit(prices));
+    }
+
+    @Test
+    public void test2() {
+        prices = new int[]{7, 6, 4, 3, 1};
+        assertEquals(0, solution1.maxProfit(prices));
+        assertEquals(0, solution2.maxProfit(prices));
+    }
+
+    @Test
+    public void test3() {
+        prices = new int[]{2, 4, 1};
+        assertEquals(2, solution1.maxProfit(prices));
+        assertEquals(2, solution2.maxProfit(prices));
+    }
+
+    @Test
+    public void test4() {
+        prices = new int[]{1, 2};
+        assertEquals(1, solution1.maxProfit(prices));
+        assertEquals(1, solution2.maxProfit(prices));
+    }
 }
