[SeongA] Week 12 solution

non-overlapping-intervals/delight010.swift

@@ -0,0 +1,22 @@
+class Solution {
+    // Time O(n log n)
+    // Space O(n)
+    func eraseOverlapIntervals(_ intervals: [[Int]]) -> Int {
+        if intervals.count < 2 { return 0 }
+
+        var answer = 0
+        let intervals = intervals.sorted { $0[1] < $1[1] }
+        var currentInterval = intervals[0]
+
+        for i in 1..<intervals.count {
+            if currentInterval[1] <= intervals[i][0] {
+                currentInterval = intervals[i]
+            } else {
+                answer += 1
+            }
+        }
+
+        return answer
+    }
+}
+

remove-nth-node-from-end-of-list/delight010.swift

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+public class ListNode {
+    public var val: Int
+    public var next: ListNode?
+    public init() { self.val = 0; self.next = nil; }
+    public init(_ val: Int) { self.val = val; self.next = nil; }
+    public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
+}
+
+class Solution {
+    // Time O(n)
+    // Space O(1)
+    func removeNthFromEnd(_ head: ListNode?, _ n: Int) -> ListNode? {
+        var slow: ListNode? = head
+        var fast: ListNode? = head
+        var prev: ListNode?
+
+        for _ in 1...n {
+            fast = fast?.next
+        }
+
+        while fast != nil {
+            prev = slow
+            slow = slow?.next
+            fast = fast?.next
+        }
+
+        if prev != nil {
+            prev?.next = slow?.next
+        } else {
+            return head?.next
+        }
+
+        return head
+    }
+}
+

same-tree/delight010.swift

@@ -0,0 +1,37 @@
+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 best O(log n)
+    // Space worst O(n)
+    func isSameTree(_ p: TreeNode?, _ q: TreeNode?) -> Bool {
+        return dfs(p, q)
+    }
+
+    private func dfs(_ p: TreeNode?, _ q: TreeNode?) -> Bool {
+        if p == nil && q == nil {
+            return true
+        }
+
+        guard let p = p else { return false }
+        guard let q = q else { return false }
+
+        if p.val != q.val {
+            return false
+        }
+
+        return dfs(p.left, q.left) && dfs(p.right, q.right)
+    }
+}
+