algorithm001 · GeekUniversity · May 13, 2019 · May 11, 2019 · May 12, 2019 · May 12, 2019
diff --git a/Week_04/id_31/LeetCode_169_031.swift b/Week_04/id_31/LeetCode_169_031.swift
@@ -0,0 +1,66 @@
+//
+//  LeetCode_169_031.swift
+//  TestCoding
+//
+//  Created by 龚欢 on 2019/5/12.
+//  Copyright © 2019 龚欢. All rights reserved.
+//
+
+import Foundation
+
+// 哈希Map
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        guard !nums.isEmpty else { return -1 }
+        var res: [Int: Int] = [:]
+        for v in nums {
+            if var data = res[v] {
+                data += 1
+                res[v] = data
+            } else {
+                res[v] = 1
+            }
+            if res[v]! > nums.count / 2 { return v }
+        }
+        return -1
+    }
+}
+
+// 排序
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        guard !nums.isEmpty else { return -1 }
+        let sorted = nums.sorted{ $0 < $1 }
+        return sorted[(0+sorted.count - 1) / 2]
+    }
+}
+
+// 分治算法
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        return major(nums, 0, nums.count - 1).value
+    }
+
+    private func major(_ nums: [Int], _ from: Int, _ to: Int) -> (value: Int, count: Int) {
+        guard from < to else { return (value: nums[from], 1)}
+        let mid = from + (to - from) / 2
+        let leftData = major(nums, from, mid)
+        let rightData = major(nums, mid+1, to)
+        if leftData.value == rightData.value {
+            return (value: leftData.value, count: leftData.count + rightData.count)
+        }
+
+
+        if (leftData.count > rightData.count) {
+            return (value: leftData.value, count: leftData.count + findNum(leftData.value, Array(nums[mid+1...to])))
+        } else {
+            return (value: rightData.value, count: rightData.count + findNum(rightData.value, Array(nums[from...mid])))
+        }
+    }
+
+    private func findNum(_ value: Int, _ nums: [Int]) -> Int {
+        var res: Int = 0
+        _ = nums.map { if ($0 == value) { res += 1 }}
+        return res
+    }
+}
diff --git a/Week_04/id_31/LeetCode_455_031.swift b/Week_04/id_31/LeetCode_455_031.swift
@@ -0,0 +1,36 @@
+//
+//  LeetCode_455_031.swift
+//  TestCoding
+//
+//  Created by 龚欢 on 2019/5/12.
+//  Copyright © 2019 龚欢. All rights reserved.
+//
+
+import Foundation
+
+class Solution {
+    func findContentChildren(_ g: [Int], _ s: [Int]) -> Int {
+        var res: Int = 0
+        var sortedG = g.sorted { $0 < $1 }
+        var sortedS = s.sorted { $0 < $1 }
+        // 先满足胃口最小的孩子
+        for i in 0..<sortedG.count {
+            let gg = sortedG[i]
+
+            var sIndex = 0
+            while sIndex <= sortedS.count - 1 {
+                let ss = sortedS[sIndex]
+                if (ss >= gg) {
+                    // 找到满足这个孩子胃口的食物了,并且在食物列表中移除它
+                    sortedS.remove(at: sIndex)
+                    // 记录一下满足孩子的个数
+                    res += 1
+                    // 退出此次循环
+                    break
+                }
+                sIndex += 1
+            }
+        }
+        return res
+    }
+}
diff --git a/Week_04/id_31/LeetCode_720_031.swift b/Week_04/id_31/LeetCode_720_031.swift
@@ -0,0 +1,36 @@
+//
+//  LeetCode_720_031.swift
+//  TestCoding
+//
+//  Created by 龚欢 on 2019/5/11.
+//  Copyright © 2019 龚欢. All rights reserved.
+//
+
+import Foundation
+
+class Solution {
+    func longestWord(_ words: [String]) -> String {
+        let sortedWords = Set(words).sorted {
+            if $0.count == $1.count {
+                return $0 < $1
+            } else {
+                return $0.count > $1.count
+            }
+        }
+        var errorDatas: Set<String> = []
+        for key in sortedWords {
+            if (errorDatas.contains(key)) { continue }
+            for i in 1...key.count {
+                let subString = String(key[key.startIndex..<key.index(key.startIndex, offsetBy: i)])
+                if (sortedWords.contains(subString)) {
+                    if i == key.count { return key }
+                    continue
+                } else {
+                    errorDatas.insert(key)
+                    break
+                }
+            }
+        }
+        return ""
+    }
+}
diff --git a/Week_04/id_31/LeetCode_784_031.swift b/Week_04/id_31/LeetCode_784_031.swift
@@ -0,0 +1,47 @@
+//
+//  LeetCode_784_031.swift
+//  TestCoding
+//
+//  Created by 龚欢 on 2019/5/12.
+//  Copyright © 2019 龚欢. All rights reserved.
+//
+
+import Foundation
+
+class Solution {
+    var m: [String] = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
+    var n: [String] = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
+    var res: Set<String> = []
+    func letterCasePermutation(_ S: String) -> [String] {
+        var s = S
+        _ = find(&s, 0)
+        return Array(res)
+    }
+
+    private func find(_ S: inout String, _ from: Int) {
+        if from == S.count {
+            return
+        }
+        guard let offSetStart = S.index(S.startIndex, offsetBy: from, limitedBy: S.endIndex), let offSetEnd   = S.index(offSetStart, offsetBy: 1, limitedBy: S.endIndex) else { return }
+        let findRange = offSetStart..<offSetEnd
+        let findWord = String(S[findRange])
+        if m.contains(findWord) || n.contains(findWord) {
+            // 可以切换大小写
+            // 1. 不切换大小写
+            res.insert(S)
+            find(&S, from + 1)
+
+            // 2. 切换大小写
+            if (m.contains(findWord)) {
+                S = S.replacingOccurrences(of: findWord, with: n[m.index(of: findWord)!], options:[], range: findRange)
+            } else if (n.contains(findWord)) {
+                S = S.replacingOccurrences(of: findWord, with: m[n.index(of: findWord)!], options:[], range: findRange)
+            }
+            res.insert(S)
+            find(&S, from + 1)
+        } else {
+            res.insert(S)
+            find(&S, from + 1)
+        }
+    }
+}