2 problem

Author: partho-maple

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/1522_Diameter_of_N-Ary_Tree.swift

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+// My initial solution. 37 / 38 test cases passed. https://tinyurl.com/y2wfypuh
+class Solution {
+ func diameter(_ root: Node?) -> Int {
+ guard let root = root else {
+ return 0
+ }
+ var (excludingThisNode, asRoot, asBranch) = diameterDFSHelper(root)
+ return [excludingThisNode, asRoot, asBranch].max()!
+ }
+ 
+ func diameterDFSHelper(_ root: Node) -> (Int, Int, Int) {
+ guard !root.children.isEmpty else {
+ return (0, 0, 0)
+ }
+ 
+ var (excludingThisNode, max1, max2) = (0, 0, 0)
+ for node in root.children {
+ let (_, asRootCurr, asBranchCurr) = diameterDFSHelper(node)
+ excludingThisNode = max(excludingThisNode, asRootCurr)
+ if asBranchCurr > max1 {
+ max2 = max1
+ max1 = asBranchCurr
+ } else if asBranchCurr > max2 {
+ max2 = asBranchCurr
+ }
+ }
+ 
+ if root.children.count == 1 {
+ return (excludingThisNode, 1 + max1, 1 + max1)
+ } else {
+ return (excludingThisNode, 2 + max1 + max2, 1 + max1)
+ }
+ }
+}
+
+// https://tinyurl.com/y5oyyjpf
+class Solution {
+ var result = 0
+ func diameter(_ root: Node?) -> Int {
+ guard let root = root else { return 0 }
+ getHeightDFSHelper(root)
+ return result
+ }
+ 
+ func getHeightDFSHelper(_ root: Node?) -> Int {
+ guard let root = root else { return 0 }
+ var max1Height = 0
+ var max2Height = 0
+ for child in root.children {
+ let currentHeight = getHeightDFSHelper(child)
+ if currentHeight > max1Height {
+ max2Height = max1Height
+ max1Height = currentHeight
+ } else if currentHeight > max2Height {
+ max2Height = currentHeight
+ }
+ }
+ result = max(result, max1Height + max2Height)
+ return max(max1Height, max2Height) + 1
+ }
+}

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/983_Minimum_Cost_For_Tickets.swift

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+
+// Main idea: https://tinyurl.com/yy63r8cy
+class Solution {
+ func mincostTickets(_ days: [Int], _ costs: [Int]) -> Int {
+ var dp = Array(repeating: 0, count: 396) // 365 + 31
+ var daysSet = Set<Int>()
+ for day in days {
+ daysSet.insert(day)
+ }
+ 
+ for i in 31...395 {
+ if !daysSet.contains(i - 30) {
+ dp[i] = dp[i - 1]
+ } else {
+ dp[i] = [(dp[i - 1] + costs[0]), (dp[i - 7] + costs[1]), (dp[i - 30] + costs[2])].min()!
+ }
+ }
+ return dp.last!
+ }
+}
+
+// Main idea: https://tinyurl.com/yy63r8cy
+class Solution {
+ func mincostTickets(_ days: [Int], _ costs: [Int]) -> Int {
+ var minCost = 0, last7daysQueue = [(Int, Int)](), last30daysQueue = [(Int, Int)]() // (day, cost) tuple
+ for day in days {
+ while !last7daysQueue.isEmpty && (last7daysQueue.first!.0 + 7) <= day {
+ last7daysQueue.removeFirst()
+ }
+ while !last30daysQueue.isEmpty && (last30daysQueue.first!.0 + 30) <= day {
+ last30daysQueue.removeFirst()
+ }
+ last7daysQueue.append((day, minCost + costs[1]))
+ last30daysQueue.append((day, minCost + costs[2]))
+ minCost = [minCost + costs.first!, last7daysQueue.first!.1, last30daysQueue.first!.1].min()!
+ }
+ return minCost
+ }
+}