diff --git a/lcci/17.21.Volume of Histogram/README.md b/lcci/17.21.Volume of Histogram/README.md
index f7efe350feec0..7b4ffd2cfe962 100644
--- a/lcci/17.21.Volume of Histogram/README.md	
+++ b/lcci/17.21.Volume of Histogram/README.md	
@@ -156,6 +156,38 @@ public class Solution {
 }
 ```
 
+```swift
+class Solution {
+    func trap(_ height: [Int]) -> Int {
+        let n = height.count
+        if n < 3 {
+            return 0
+        }
+
+        var left = [Int](repeating: 0, count: n)
+        var right = [Int](repeating: 0, count: n)
+
+        left[0] = height[0]
+        right[n - 1] = height[n - 1]
+
+        for i in 1..<n {
+            left[i] = max(left[i - 1], height[i])
+        }
+
+        for i in stride(from: n - 2, through: 0, by: -1) {
+            right[i] = max(right[i + 1], height[i])
+        }
+
+        var ans = 0
+        for i in 0..<n {
+            ans += min(left[i], right[i]) - height[i]
+        }
+
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->
diff --git a/lcci/17.21.Volume of Histogram/README_EN.md b/lcci/17.21.Volume of Histogram/README_EN.md
index c934f608d3a0d..a0557cd372146 100644
--- a/lcci/17.21.Volume of Histogram/README_EN.md	
+++ b/lcci/17.21.Volume of Histogram/README_EN.md	
@@ -150,6 +150,38 @@ public class Solution {
 }
 ```
 
+```swift
+class Solution {
+    func trap(_ height: [Int]) -> Int {
+        let n = height.count
+        if n < 3 {
+            return 0
+        }
+
+        var left = [Int](repeating: 0, count: n)
+        var right = [Int](repeating: 0, count: n)
+
+        left[0] = height[0]
+        right[n - 1] = height[n - 1]
+
+        for i in 1..<n {
+            left[i] = max(left[i - 1], height[i])
+        }
+
+        for i in stride(from: n - 2, through: 0, by: -1) {
+            right[i] = max(right[i + 1], height[i])
+        }
+
+        var ans = 0
+        for i in 0..<n {
+            ans += min(left[i], right[i]) - height[i]
+        }
+
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->
diff --git a/lcci/17.21.Volume of Histogram/Solution.swift b/lcci/17.21.Volume of Histogram/Solution.swift
new file mode 100644
index 0000000000000..61d30a3e741d4
--- /dev/null
+++ b/lcci/17.21.Volume of Histogram/Solution.swift	
@@ -0,0 +1,29 @@
+class Solution {
+    func trap(_ height: [Int]) -> Int {
+        let n = height.count
+        if n < 3 {
+            return 0
+        }
+        
+        var left = [Int](repeating: 0, count: n)
+        var right = [Int](repeating: 0, count: n)
+        
+        left[0] = height[0]
+        right[n - 1] = height[n - 1]
+
+        for i in 1..<n {
+            left[i] = max(left[i - 1], height[i])
+        }
+
+        for i in stride(from: n - 2, through: 0, by: -1) {
+            right[i] = max(right[i + 1], height[i])
+        }
+
+        var ans = 0
+        for i in 0..<n {
+            ans += min(left[i], right[i]) - height[i]
+        }
+        
+        return ans
+    }
+}
\ No newline at end of file