feat: add swift implementation to lcp problem: No.22 (#3772)

Author: klever34

lcp/LCP 22. 黑白方格画/README.md

@@ -195,6 +195,41 @@ function paintingPlan(n: number, k: number): number {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func paintingPlan(_ n: Int, _ k: Int) -> Int {
+        if k == 0 || k == n * n {
+            return 1
+        }
+        
+        func combination(_ n: Int, _ r: Int) -> Int {
+            guard r <= n else { return 0 }
+            if r == 0 || r == n { return 1 }
+            var result = 1
+            for i in 0..<r {
+                result = result * (n - i) / (i + 1)
+            }
+            return result
+        }
+        
+        var ans = 0
+        
+        for i in 0...n {
+            for j in 0...n {
+                let paintedCells = n * (i + j) - i * j
+                if paintedCells == k {
+                    ans += combination(n, i) * combination(n, j)
+                }
+            }
+        }
+        
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcp/LCP 22. 黑白方格画/Solution.swift

@@ -0,0 +1,30 @@
+class Solution {
+    func paintingPlan(_ n: Int, _ k: Int) -> Int {
+        if k == 0 || k == n * n {
+            return 1
+        }
+        
+        func combination(_ n: Int, _ r: Int) -> Int {
+            guard r <= n else { return 0 }
+            if r == 0 || r == n { return 1 }
+            var result = 1
+            for i in 0..<r {
+                result = result * (n - i) / (i + 1)
+            }
+            return result
+        }
+        
+        var ans = 0
+        
+        for i in 0...n {
+            for j in 0...n {
+                let paintedCells = n * (i + j) - i * j
+                if paintedCells == k {
+                    ans += combination(n, i) * combination(n, j)
+                }
+            }
+        }
+        
+        return ans
+    }
+}