feat: add swift implementation to lcci problem: No.17.06

lcci/17.06.Number Of 2s In Range/README.md

@@ -193,6 +193,45 @@ func numberOf2sInRange(n int) int {
 }
 ```
 
+```swift
+class Solution {
+    private var a = [Int](repeating: 0, count: 12)
+    private var dp = [[Int]](repeating: [Int](repeating: -1, count: 12), count: 12)
+
+    func numberOf2sInRange(_ n: Int) -> Int {
+        var n = n
+        var len = 0
+        while n > 0 {
+            len += 1
+            a[len] = n % 10
+            n /= 10
+        }
+        for i in 0..<12 {
+            dp[i] = [Int](repeating: -1, count: 12)
+        }
+        return dfs(len, 0, true)
+    }
+
+    private func dfs(_ pos: Int, _ cnt: Int, _ limit: Bool) -> Int {
+        if pos <= 0 {
+            return cnt
+        }
+        if !limit && dp[pos][cnt] != -1 {
+            return dp[pos][cnt]
+        }
+        let up = limit ? a[pos] : 9
+        var ans = 0
+        for i in 0...up {
+            ans += dfs(pos - 1, cnt + (i == 2 ? 1 : 0), limit && i == up)
+        }
+        if !limit {
+            dp[pos][cnt] = ans
+        }
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.06.Number Of 2s In Range/README_EN.md

@@ -196,6 +196,45 @@ func numberOf2sInRange(n int) int {
 }
 ```
 
+```swift
+class Solution {
+    private var a = [Int](repeating: 0, count: 12)
+    private var dp = [[Int]](repeating: [Int](repeating: -1, count: 12), count: 12)
+
+    func numberOf2sInRange(_ n: Int) -> Int {
+        var n = n
+        var len = 0
+        while n > 0 {
+            len += 1
+            a[len] = n % 10
+            n /= 10
+        }
+        for i in 0..<12 {
+            dp[i] = [Int](repeating: -1, count: 12)
+        }
+        return dfs(len, 0, true)
+    }
+
+    private func dfs(_ pos: Int, _ cnt: Int, _ limit: Bool) -> Int {
+        if pos <= 0 {
+            return cnt
+        }
+        if !limit && dp[pos][cnt] != -1 {
+            return dp[pos][cnt]
+        }
+        let up = limit ? a[pos] : 9
+        var ans = 0
+        for i in 0...up {
+            ans += dfs(pos - 1, cnt + (i == 2 ? 1 : 0), limit && i == up)
+        }
+        if !limit {
+            dp[pos][cnt] = ans
+        }
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.06.Number Of 2s In Range/Solution.swift

@@ -0,0 +1,36 @@
+class Solution {
+    private var a = [Int](repeating: 0, count: 12)
+    private var dp = [[Int]](repeating: [Int](repeating: -1, count: 12), count: 12)
+
+    func numberOf2sInRange(_ n: Int) -> Int {
+        var n = n
+        var len = 0
+        while n > 0 {
+            len += 1
+            a[len] = n % 10
+            n /= 10
+        }
+        for i in 0..<12 {
+            dp[i] = [Int](repeating: -1, count: 12)
+        }
+        return dfs(len, 0, true)
+    }
+
+    private func dfs(_ pos: Int, _ cnt: Int, _ limit: Bool) -> Int {
+        if pos <= 0 {
+            return cnt
+        }
+        if !limit && dp[pos][cnt] != -1 {
+            return dp[pos][cnt]
+        }
+        let up = limit ? a[pos] : 9
+        var ans = 0
+        for i in 0...up {
+            ans += dfs(pos - 1, cnt + (i == 2 ? 1 : 0), limit && i == up)
+        }
+        if !limit {
+            dp[pos][cnt] = ans
+        }
+        return ans
+    }
+}