Merge pull request #1923 from delight010/main

[SeongA] week 10 solutions

Author: delight010

course-schedule/delight010.swift

@@ -0,0 +1,38 @@
+class Solution {
+    // Time  O(V + E)
+    // Space  O(V + E)
+    func canFinish(_ numCourses: Int, _ prerequisites: [[Int]]) -> Bool {
+        var indegree: [Int] = Array(repeating: 0, count: numCourses)
+        var queue: [Int] = []
+        var graph: [[Int]] = Array(repeating: [], count: numCourses)
+        
+        for i in 0..<prerequisites.count {
+            let degree = prerequisites[i].first!
+            let graphIndex = prerequisites[i][1]
+            indegree[degree] += 1
+            graph[graphIndex].append(degree)
+        }
+        
+        for i in 0..<indegree.count {
+            if indegree[i] == 0 {
+                queue.append(i)
+            }
+        }
+        
+        var count = 0
+        
+        while !queue.isEmpty {
+            let current = queue.removeFirst()
+            count += 1
+            for i in graph[current] {
+                indegree[i] -= 1
+                if indegree[i] == 0 {
+                    queue.append(i)
+                }
+            }
+        }
+        
+        return count == numCourses
+    }
+}
+ 

invert-binary-tree/delight010.swift

@@ -0,0 +1,41 @@
+public class TreeNode {
+    public var val: Int
+    public var left: TreeNode?
+    public var right: TreeNode?
+    public init() { self.val = 0; self.left = nil; self.right = nil; }
+    public init( val: Int) { self.val = val; self.left = nil; self.right = nil; }
+    public init( val: Int, * left: TreeNode?, * right: TreeNode?) {
+        self.val = val
+        self.left = left
+        self.right = right
+    }
+}
+
+class Solution {
+    // Time O(n)
+    // Space O(n)
+    func invertTree(_ root: TreeNode?) -> TreeNode? {
+        guard let root = root else {
+            return nil
+        }
+
+        var queue: [TreeNode] = [root]
+
+        while queue.isEmpty == false {
+            let current = queue.removeFirst()
+
+            if let left = current.left {
+                queue.append(left)
+            }
+
+            if let right = current.right {
+                queue.append(right)
+            }
+
+            (current.left, current.right) = (current.right, current.left)
+        }
+
+        return root
+    }
+}
+ 

jump-game/delight010.swift

@@ -0,0 +1,16 @@
+class Solution {
+    // Time O(n)
+    // Space O(1)
+    func canJump(_ nums: [Int]) -> Bool {
+        var maxReachIndex = 0
+        for i in 0..<nums.count {
+            if i > maxReachIndex {
+                return false
+            }
+            maxReachIndex = max(maxReachIndex, nums[i] + i)
+        }
+        
+        return maxReachIndex >= nums.count - 1
+    }
+}
+