diff --git a/swift/42-Trapping-Rain-Water.swift b/swift/42-Trapping-Rain-Water.swift
new file mode 100644
index 000000000..8fd569e30
--- /dev/null
+++ b/swift/42-Trapping-Rain-Water.swift
@@ -0,0 +1,30 @@
+class Solution {
+    func trap(_ height: [Int]) -> Int {
+        if height == nil {
+            return 0
+        }
+        
+        var res = 0
+        var l = 0
+        var r = height.count - 1
+        
+        var leftMax = height[l]
+        var rightMax = height[r]
+        
+        while l < r {
+            if leftMax < rightMax {
+                l += 1
+                leftMax = max(leftMax, height[l])
+                res += leftMax - height[l]
+            } else {
+                r -= 1
+                rightMax = max(rightMax, height[r])
+                res += rightMax - height[r]
+            }
+        }
+        
+        return res
+        
+    }
+    
+}