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Algorithms/14. Longest Common Prefix/main.swift

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+//
+//  main.swift
+//  14. Longest Common Prefix
+//
+//  Created by ryan on 10/05/2017.
+//  Copyright © 2017 ryan. All rights reserved.
+//
+
+class Solution {
+//    func longestCommonPrefix(_ strs: [String]) -> String {
+//        let totalCount = strs.count
+//        if totalCount == 0 {
+//            return ""
+//        }
+//
+//        let firstString = strs[0]
+//
+//        var commonPrefixEndIndex = firstString.characters.count
+//        var index = 0
+//        while commonPrefixEndIndex > index {
+//            var qualifiedC: Character? = nil
+//            for i in 0..<totalCount {
+//                let str = strs[i]
+//                
+//                let currentCount = str.characters.count
+//                commonPrefixEndIndex = min(commonPrefixEndIndex, currentCount)
+//                if index >= currentCount {
+//                    qualifiedC = nil
+//                    break
+//                }
+//                
+//                let strC = str[str.index(str.startIndex, offsetBy: index)]
+//                
+//                if i == 0 && qualifiedC == nil {
+//                    qualifiedC = strC
+//                } else if qualifiedC != strC {
+//                    commonPrefixEndIndex = index
+//                    break
+//                }
+//            }
+//            
+//            if  qualifiedC == nil {
+//                commonPrefixEndIndex = index
+//                break
+//            }
+//            
+//            index += 1
+//        }
+//        
+//        return firstString[firstString.startIndex..<firstString.index(firstString.startIndex, offsetBy: commonPrefixEndIndex)]
+//    }
+
+    func longestCommonPrefix(_ strs: [String]) -> String {
+        if strs.isEmpty {
+            return ""
+        }
+
+        var commonPrefix = strs[0]
+        for i in 1..<strs.count {
+            let comparingStr = strs[i]
+            if comparingStr.characters.count < commonPrefix.characters.count {
+                commonPrefix = commonPrefix[commonPrefix.startIndex..<commonPrefix.index(commonPrefix.startIndex, offsetBy: comparingStr.characters.count)]
+            }
+
+            if commonPrefix == "" {
+                return commonPrefix
+            }
+
+            while !comparingStr.hasPrefix(commonPrefix) && commonPrefix != "" {
+                commonPrefix = commonPrefix[commonPrefix.startIndex..<commonPrefix.index(commonPrefix.startIndex, offsetBy: commonPrefix.characters.count - 1)]
+            }
+        }
+
+        return commonPrefix
+    }
+}
+
+let solution = Solution()
+
+//print(solution.longestCommonPrefix(["abab","aba",""]))
+//print(solution.longestCommonPrefix(["aca","cba"]))
+print(solution.longestCommonPrefix(["a","b"]))
+

Algorithms/540. Single Element in a Sorted Array/main.swift

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+//
+//  main.swift
+//  540. Single Element in a Sorted Array
+//
+//  Created by ryan on 10/05/2017.
+//  Copyright © 2017 ryan. All rights reserved.
+//
+
+class Solution {
+    func singleNonDuplicate(_ nums: [Int]) -> Int {
+
+        let low = 0
+        let high = nums.count/2
+
+        let index = singleNonDuplicate(nums, low: low, high: high)
+        return nums[index]
+    }
+
+    func singleNonDuplicate(_ nums: [Int], low: Int, high: Int) -> Int {
+        let mid = (low + high)/2
+        if low < high {
+            if nums[2 * mid] != nums[2 * mid + 1] {
+                return singleNonDuplicate(nums, low: low, high: mid)
+            } else {
+                return singleNonDuplicate(nums, low: mid + 1, high: high)
+            }
+        }
+
+        return 2 * low
+    }
+
+}
+
+
+let solution = Solution()
+
+//let array = [1,1,2,3,3,4,4,8,8]
+//let array = [1,1,2]
+let array = [1,1,2,3,3,4,4,8,8]
+print(solution.singleNonDuplicate(array))