Add Trapping Rainwater problem implementation (Two Pointer Approach)

src/main/java/com/thealgorithms/searches/TrappingRainwater.java

@@ -0,0 +1,48 @@
+package com.thealgorithms.searches;
+/**
+ * Trapping Rainwater Problem
+ * Given an array of non-negative integers representing the height of bars,
+ * compute how much water it can trap after raining.
+ *
+ * Example:
+ * Input: [4,2,0,3,2,5]
+ * Output: 9
+ *
+ * Time Complexity: O(n)
+ * Space Complexity: O(1)
+ *
+ * Reference: https://en.wikipedia.org/wiki/Trapping_rain_water
+ */
+public final class TrappingRainwater {
+
+    private TrappingRainwater() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+
+    public static int trap(int[] height) {
+        int left = 0;
+        int right = height.length - 1;
+        int leftMax = 0;
+        int rightMax = 0;
+        int result = 0;
+
+        while (left < right) {
+            if (height[left] < height[right]) {
+                if (height[left] >= leftMax) {
+                    leftMax = height[left];
+                } else {
+                    result += leftMax - height[left];
+                }
+                left++;
+            } else {
+                if (height[right] >= rightMax) {
+                    rightMax = height[right];
+                } else {
+                    result += rightMax - height[right];
+                }
+                right--;
+            }
+        }
+        return result;
+    }
+}