add ZigZag

Algorithms/223. Rectangle Area/main.swift

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+//
+//  main.swift
+//  223. Rectangle Area
+//
+//  Created by ryan on 23/05/2017.
+//  Copyright © 2017 ryan. All rights reserved.
+//
+
+/*
+Find the total area covered by two rectilinear rectangles in a 2D plane.
+
+Each rectangle is defined by its bottom left corner and top right corner as shown in the figure.
+
+Rectangle Area
+Assume that the total area is never beyond the maximum possible value of int.
+*/
+
+

Algorithms/23. Merge k Sorted Lists/main.swift

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+//
+//  main.swift
+//  23. Merge k Sorted Lists
+//
+//  Created by ryan on 23/05/2017.
+//  Copyright © 2017 ryan. All rights reserved.
+//
+
+/**
+ * 
+ * Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
+ *
+ */
+
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public var val: Int
+ *     public var next: ListNode?
+ *     public init(_ val: Int) {
+ *         self.val = val
+ *         self.next = nil
+ *     }
+ * }
+ */
+
+public class ListNode {
+    public var val: Int
+    public var next: ListNode?
+    public init(_ val: Int) {
+        self.val = val
+        self.next = nil
+    }
+}
+
+//TODO: 解法超时, 需要优化
+class Solution {
+    func mergeKLists(_ lists: [ListNode?]) -> ListNode? {
+        if lists.count == 0 {
+            return nil
+        } else if lists.count == 1 {
+            return lists.first!
+        }
+        var listNode: ListNode? = nil
+        for list in lists {
+            listNode = mergeList(listNode, list)
+        }
+
+        return listNode
+    }
+
+    func mergeList(_ listA: ListNode?, _ listB: ListNode?) -> ListNode? {
+        if listA == nil {
+            return listB
+        } else if listB == nil {
+            return listA
+        }
+
+        if listA!.val < listB!.val {
+            let right = mergeList(listA!.next, listB)
+            listA?.next = right
+            return listA
+        } else {
+            let right = mergeList(listB!.next, listA)
+            listB?.next = right
+            return listB
+        }
+    }
+}
+
+func createLists(_ values: [[Int]]) -> [ListNode?] {
+    var lists: [ListNode?] = [ListNode?]()
+
+    for value in values {
+        let list = createList(value)
+        lists.append(list)
+    }
+    return lists
+}
+
+func createList(_ values: [Int]) -> ListNode {
+    let first = ListNode(values[0])
+    var pivot = first
+    for i in 1..<values.count {
+        pivot.next = ListNode(values[i])
+        pivot = pivot.next!
+    }
+    return first
+}
+
+
+let soluition = Solution()
+let lists = createLists([[7],[49],[73],[58],[30],[72],[44],[78],[23]])
+soluition.mergeKLists(lists)

Algorithms/6. ZigZag Conversion/main.swift

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+//
+//  main.swift
+//  6. ZigZag Conversion
+//
+//  Created by ryan on 24/05/2017.
+//  Copyright © 2017 ryan. All rights reserved.
+//
+
+/*
+The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)
+
+P   A   H   N
+A P L S I I G
+Y   I   R
+And then read line by line: "PAHNAPLSIIGYIR"
+Write the code that will take a string and make this conversion given a number of rows:
+
+string convert(string text, int nRows);
+convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".
+*/
+
+
+// 常规方法按照Z型走势依次给字符串赋值
+class Solution {
+    func convert(_ s: String, _ numRows: Int) -> String {
+        var results = [[Character]]()
+
+        var row = 0
+        var direction = 1
+        for c in s.characters {
+            if results.count <= row {
+               results.append([])
+            }
+            results[row].append(c)
+            if row == 0 {
+                direction = 1
+            } else if row == numRows - 1 {
+                direction = -1
+            }
+            row += direction
+        }
+
+        var result = ""
+        for r in results {
+            result += String(r)
+        }
+        return result
+    }
+}
+
+
+let solution = Solution()
+print(solution.convert("PAYPALISHIRING", 3))
+print(solution.convert("PAYPALISHIRING", 4) == "PINALSIGYAHRPI")