add Trapping Rain Water Solution

src/LeetCode.Solutions/NeetCode150/ArraysAndHashing/TrappingRainWaterSolution.cs

@@ -0,0 +1,44 @@
+namespace LeetCode.Solutions.NeetCode150.ArraysAndHashing;
+/// <summary>
+// You are given an array non-negative integers heights which represent an elevation map. Each value heights[i] represents the height of a bar, which has a width of 1.
+
+// Return the maximum area of water that can be trapped between the bars.
+/// </summary>
+[Level(Level.Hard)]
+public class TrappingRainWaterSolution
+{
+    [TimeComplexity("O(n)")]
+    [SpaceComplexity("O(1)")]
+    public int Trap(int[] height)
+    {
+
+        if (height == null || height.Length == 0)
+        {
+            return 0;
+        }
+
+        int left = 0;
+        int right = height.Length - 1;
+
+        int leftMax = height[left];
+        int rightMax = height[right];
+        int result = 0;
+
+        while (left < right)
+        {
+            if (leftMax < rightMax)
+            {
+                left++;
+                leftMax = Math.Max(leftMax, height[left]);
+                result += leftMax - height[left];
+            }
+            else
+            {
+                right--;
+                rightMax = Math.Max(rightMax, height[right]);
+                result += rightMax - height[right];
+            }
+        }
+        return result;
+    }
+}

src/LeetCode.Tests/NeetCode150/TwoPointers/TrappingRainWaterTests.cs

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+using LeetCode.Solutions.NeetCode150.ArraysAndHashing;
+
+namespace LeetCode.Tests.NeetCode150.TwoPointers;
+
+public class TrappingRainWaterTests
+{
+    [Test]
+    public void Case1()
+    {
+        var solution = new TrappingRainWaterSolution();
+        var result = solution.Trap([0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]);
+
+        result.Should().Be(6);
+    }
+
+    [Test]
+    public void Case2()
+    {
+        var solution = new TrappingRainWaterSolution();
+        var result = solution.Trap([4, 2, 0, 3, 2, 5]);
+
+        result.Should().Be(9);
+    }
+
+    [Test]
+    public void Case3()
+    {
+        var solution = new TrappingRainWaterSolution();
+        var result = solution.Trap([1, 2, 3, 4, 5]);
+
+        result.Should().Be(0);
+    }
+
+    [Test]
+    public void Case4()
+    {
+        var solution = new TrappingRainWaterSolution();
+        var result = solution.Trap([5, 4, 3, 2, 1]);
+
+        result.Should().Be(0);
+    }
+}