Added TrappingRainWater solution

Author: xurten

CodingInterview/CodingInterview/Tests.cs

@@ -1,4 +1,5 @@
 using NUnit.Framework;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 
@@ -66,6 +67,24 @@ int[] MoveZeros(int[] arrayOfNumbers)
  return listOfElements.ToArray();
  }
 
+ int GetTrappingRainWater(int[] elevationMap)
+ {
+ if (elevationMap == null || elevationMap.Length == 0)
+ return 0;
+ int waterToDrop = 0;
+ int level = 0;
+ int left = 0;
+ int right = elevationMap.Length - 1;
+ while(left < right)
+ {
+ int lower = elevationMap[elevationMap[left] < elevationMap[right] ? left++ : right--];
+ level = Math.Max(lower, level);
+ waterToDrop += level - lower;
+ Console.WriteLine($"left{left} right{right} lower {lower} level {level} waterToDrop {waterToDrop}");
+ }
+ return waterToDrop;
+ }
+
  [Test]
  public void RemoveDuplicatesFromSortedArray_1()
  {
@@ -110,5 +129,16 @@ public void MoveZeros_4()
 
  Assert.AreEqual(expectedArrayWithZerosInTheEnd, arrayWithRemoveElement);
  }
+
+ [Test]
+ public void TrappingRainWater_6()
+ {
+ var elevationMap = new int[] {0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1 };
+ var expectedValue = 6;
+
+ var rainWaterValue = GetTrappingRainWater(elevationMap);
+
+ Assert.AreEqual(expectedValue, rainWaterValue);
+ }
  }
 }