ZigZag Conversion.

Author: recherst

Medium/5.Longest Palindromic Substring.playground/Contents.swift

@@ -22,7 +22,7 @@ class Solution {
     private var rightPosition = 0
     private var maxLength = 0
     func longestPalindrome(_ s: String) -> String {
-        let characterArr = s.map { $0 }
+        let characterArr = Array(s)
         for i in 0..<s.count {
             var index1 = i
             var index2 = i

Medium/6.ZigZag Conversion.playground/Contents.swift

@@ -0,0 +1,64 @@
+/**
+ 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 s, int numRows);
+  
+
+ Example 1:
+ Input: s = "PAYPALISHIRING", numRows = 3
+ Output: "PAHNAPLSIIGYIR"
+ 
+ Example 2:
+ Input: s = "PAYPALISHIRING", numRows = 4
+ Output: "PINALSIGYAHRPI"
+ Explanation:
+ P     I    N
+ A   L S  I G
+ Y A   H R
+ P     I
+ 
+ Example 3:
+ Input: s = "A", numRows = 1
+ Output: "A"
+  
+
+ Constraints:
+ - 1 <= s.length <= 1000
+ - s consists of English letters (lower-case and upper-case), ',' and '.'.
+ - 1 <= numRows <= 1000
+ */
+class Solution {
+    func convert(_ s: String, _ numRows: Int) -> String {
+        if numRows == 1 { return s }
+        var matrix: [[Character]] = Array(repeating: Array(), count: numRows)
+        
+        for (i, e) in s.enumerated() {
+            let remiander = i % (numRows - 1)
+            let quotient = i / (numRows - 1)
+            if quotient % 2 == 0 {
+                matrix[remiander].append(e)
+            } else {
+                matrix[numRows - 1 - remiander].append(e)
+            }
+        }
+        
+        var res = ""
+        for arr in matrix {
+            for e in arr {
+                res.append(e)
+            }
+        }
+        return res
+    }
+}
+
+let s = Solution()
+let r = s.convert("PAYPALISHIRING", 4)
+print(r)

Medium/6.ZigZag Conversion.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios' buildActiveScheme='true' importAppTypes='true'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Medium/6.ZigZag Conversion.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -108,3 +108,4 @@
 1. [Min Stack](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/155.Min%20Stack.playground/Contents.swift)
 2. [Longest Substring Without Repeating Characters](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/3.Longest%20Substring%20Without%20Repeating%20Characters.playground/Contents.swift)
 3. [Longest Palindromic Substring](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/5.Longest%20Palindromic%20Substring.playground/Contents.swift)
+4. [ZigZag Conversion](https://github.com/recherst/leetcode-algtorithm/blob/main/Medium/6.ZigZag%20Conversion.playground/Contents.swift)