Implement Trapped Rain Water problem using Dynamic Programming

DIRECTORY.md

@@ -250,6 +250,7 @@
             * [SubsetCount](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/SubsetCount.java)
             * [SubsetSum](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/SubsetSum.java)
             * [SumOfSubset](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/SumOfSubset.java)
+            * [TrappedRainWater](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/TrappedRainWater.java)
             * [Tribonacci](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/Tribonacci.java)
             * [UniquePaths](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/UniquePaths.java)
             * [WildcardMatching](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/dynamicprogramming/WildcardMatching.java)
@@ -578,6 +579,7 @@
             * [FloodFillTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/FloodFillTest.java)
             * [MazeRecursionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/MazeRecursionTest.java)
             * [MColoringTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/MColoringTest.java)
+            * [ParenthesesGeneratorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/ParenthesesGeneratorTest.java)
             * [PermutationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/PermutationTest.java)
             * [PowerSumTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/PowerSumTest.java)
             * [WordSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/WordSearchTest.java)
@@ -695,6 +697,7 @@
             * [PartitionProblemTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/PartitionProblemTest.java)
             * [SubsetCountTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/SubsetCountTest.java)
             * [SumOfSubsetTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/SumOfSubsetTest.java)
+            * [TrappedRainWaterTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/TrappedRainWaterTest.java)
             * [TribonacciTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/TribonacciTest.java)
             * [UniquePathsTests](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/UniquePathsTests.java)
             * [WildcardMatchingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/dynamicprogramming/WildcardMatchingTest.java)

src/main/java/com/thealgorithms/dynamicprogramming/TrappedRainWater.java

@@ -0,0 +1,42 @@
+package com.thealgorithms.dynamicprogramming;
+
+/**
+ * Utility class for calculating the amount of trapped rainwater between blocks.
+ */
+public final class TrappedRainWater {
+    private TrappedRainWater() {
+    }
+
+    /**
+     * Calculates the amount of trapped rainwater between blocks given their heights.
+     *
+     * @param height An array representing the heights of blocks.
+     * @return The total amount of trapped rainwater.
+     */
+    public static int trap(final int[] height) {
+        if (height == null || height.length == 0) return 0;
+
+        int left = 0;
+        int right = height.length - 1;
+        int leftMax = 0;
+        int rightMax = 0;
+        int trappedWater = 0;
+
+        while (left < right) {
+            if (height[left] < height[right]) {
+                if (height[left] >= leftMax)
+                    leftMax = height[left];
+                else
+                    trappedWater += leftMax - height[left];
+                left++;
+            } else {
+                if (height[right] >= rightMax)
+                    rightMax = height[right];
+                else
+                    trappedWater += rightMax - height[right];
+                right--;
+            }
+        }
+        return trappedWater;
+    }
+}

src/test/java/com/thealgorithms/dynamicprogramming/TrappedRainWaterTest.java

@@ -0,0 +1,22 @@
+package com.thealgorithms.dynamicprogramming;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class TrappedRainWaterTest {
+    @ParameterizedTest
+    @MethodSource("testCases")
+    void testTrappedRainWater(int[] heights, int expected) {
+        assertEquals(expected, TrappedRainWater.trap(heights));
+    }
+
+    private static Stream<Arguments> testCases() {
+        return Stream.of(Arguments.of(new int[] {0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1}, 6), Arguments.of(new int[] {0, 2, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1}, 7), Arguments.of(new int[] {4, 2, 0, 3, 2, 5}, 9), Arguments.of(new int[] {3, 2, 1, 0, 1, 2, 3}, 9),
+            Arguments.of(new int[] {5, 4, 3, 2, 1, 2, 3, 4, 5}, 16), Arguments.of(null, 0), // Test case for null input
+            Arguments.of(new int[] {}, 0));
+    }
+}