[String] add Solution to Text Justification

String/TextJustification.swift

@@ -0,0 +1,79 @@
+/**
+ * Question Link: https://leetcode.com/problems/text-justification/
+ * Primary idea: Iterate the words, keep track of the index of first word and the length 
+ *               of the line. Insert spaces with fix spaces and extra spaces. 
+ * Time Complexity: O(n^2), Space Complexity: O(n)
+ */
+
+class TextJustification {
+    func fullJustify(words: [String], _ maxWidth: Int) -> [String] {
+        var res = [String]()
+        var count = 0, last = 0
+
+        guard words.count > 0 && maxWidth >= 0 else {
+            return res
+        }
+
+        for i in 0 ..< words.count {
+            let wordLen = words[i].characters.count
+
+            if count + (i - last) + wordLen > maxWidth {
+                var spaceNum = 0
+                var extraNum = 0
+
+                if i - last - 1 > 0 {
+                    spaceNum = (maxWidth - count) / (i - last - 1)
+                    extraNum = (maxWidth - count) % (i - last - 1)
+                    res.append(_buildLine(words, last, i - 1, spaceNum, extraNum))
+                } else {
+                    res.append(_buildSpecialLine(words, last, last, maxWidth))
+                }
+                count = 0
+                last = i
+            }
+
+            count += wordLen
+        } 
+
+        res.append(_buildSpecialLine(words, last, words.count - 1, maxWidth))
+
+        return res
+    }
+
+    private func _buildLine(words: [String], _ start: Int, _ end: Int, _ spaceNum: Int, _ extraNum: Int) -> String {
+        var res = ""
+        var extraNum = extraNum
+
+        for i in start ... end {
+            res += words[i]
+            if i != end {
+                for _ in 1 ... spaceNum {
+                    res += " "
+                }
+                if extraNum != 0 {
+                    res += " "
+                    extraNum -= 1
+                }
+            }
+        }
+
+        return res
+    }
+
+    private func _buildSpecialLine(words: [String], _ start: Int, _ end: Int, _ lineLength: Int) -> String {
+        var res = ""
+
+        for i in start ... end {
+            res += words[i]
+            if i < end {
+                res += " "
+            }
+        }
+
+        for _ in res.characters.count ..< lineLength {
+            res += " "
+        }
+
+        return res
+    }
+}