Merge pull request #1269 from doitduri/main

[doitduri] WEEK 02 Solutions

Author: doitduri

3sum/doitduri.swift

@@ -0,0 +1,43 @@
+import Foundation
+
+class Solution {
+    func threeSum(_ nums: [Int]) -> [[Int]] {
+        var result = [[Int]]()
+        let sortedNums = nums.sorted()
+        
+        for i in 0..<sortedNums.count - 2 {
+            if i > 0 && sortedNums[i] == sortedNums[i - 1] {
+                continue
+            }
+            
+            var leftNumber = i + 1
+            var rightNumber = sortedNums.count - 1
+            
+            while leftNumber < rightNumber {
+                let sum = sortedNums[i] + sortedNums[leftNumber] + sortedNums[rightNumber]
+                
+                if sum < 0 {
+                    leftNumber += 1
+                } else if sum > 0 {
+                    rightNumber -= 1
+                } else {
+                    result.append([sortedNums[i], sortedNums[leftNumber], sortedNums[rightNumber]])
+                    
+                    while leftNumber < rightNumber && sortedNums[leftNumber] == sortedNums[leftNumber + 1] {
+                        leftNumber += 1
+                    }
+                    
+                    while leftNumber < rightNumber && sortedNums[rightNumber] == sortedNums[rightNumber - 1] {
+                        rightNumber -= 1
+                    }
+                    
+                    leftNumber += 1
+                    rightNumber -= 1
+                }
+            }
+        }
+        
+        return result
+    }
+}
+

climbing-stairs/doitduri.swift

@@ -0,0 +1,11 @@
+class Solution {
+    func climbStairs(_ n: Int) -> Int {
+        var tables = [0, 1, 2]
+        for i in 3...45 {
+            let result = tables[i-1] + tables[i-2]
+            tables.append(result)
+        }
+
+        return tables[n]
+    }
+}

product-of-array-except-self/doitduri.swift

@@ -0,0 +1,19 @@
+class Solution {
+    func productExceptSelf(_ nums: [Int]) -> [Int] {
+        let length = nums.count
+        var result = Array(repeating: 1, count: length)
+        var leftProduct = 1
+        for i in 0..<length {
+            result[i] = leftProduct
+            leftProduct *= nums[i]
+        }
+        
+        var rightProduct = 1
+        for i in (0..<length).reversed() {
+            result[i] *= rightProduct
+            rightProduct *= nums[i]
+        }
+        
+        return result
+    }
+}

valid-anagram/doitduri.swift

@@ -0,0 +1,9 @@
+class Solution {
+    func isAnagram(_ s: String, _ t: String) -> Bool {
+        guard s.count == t.count else { 
+            return false
+        }
+
+        return s.sorted() == t.sorted()
+    }
+}

validate-binary-search-tree/doitduri.swift

@@ -0,0 +1,20 @@
+class Solution {
+    
+    func isValidBST(_ root: TreeNode?) -> Bool {
+        return isValid(root, nil, nil)        
+    }
+    
+    private func isValid(_ node: TreeNode?, _ min: Int?, _ max: Int?) -> Bool {
+        guard let node = node else { return true }
+        
+        if let min = min, node.val <= min {
+            return false
+        }
+        
+        if let max = max, node.val >= max {
+            return false
+        }
+        return isValid(node.left, min, node.val) && isValid(node.right, node.val, max)
+    }
+}
+